This question is trickier than it looks! It stumped the test-makers.
Playable demonstration: Steve Phelps has made a Geogebra worksheet that you can try it out for yourself
http://tube.geogebra.org/student/m1442749
Blog post: http://mindyourdecisions.com/blog/2015/07/19/this-psat-question-stumped-almost-everyone-attaching-a-tetrahedron-to-a-pyramid-sunday-puzzle/
References:
Pyramid Power: Searching for an Error in Test Scoring with 830,000 Helpers. Howard Wainera. The American Statistician. Volume 37, Issue 1, 1983.
http://onlinelibrary.wiley.com/doi/10.1002/j.2333-8504.1981.tb01262.x/abstract
New York Times. “Youth Outwits Merit Exam, Raising 240,000 Scores.” Edward B. Fiske. March 17, 1981.
In researching this video, I found this problem was featured in the New York Times Worldplay puzzle a couple years ago: http://wordplay.blogs.nytimes.com/2013/09/23/pyramid-2/
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My Books
“The Joy of Game Theory” shows how you can use math to out-think your competition. (rated 4/5 stars on 23 reviews) https://www.amazon.com/gp/product/1500497444
“The Irrationality Illusion: How To Make Smart Decisions And Overcome Bias” is a handbook that explains the many ways we are biased about decision-making and offers techniques to make smart decisions. (rated 5/5 stars on 1 review) https://www.amazon.com/gp/product/1523231467/
“Math Puzzles Volume 1” features classic brain teasers and riddles with complete solutions for problems in counting, geometry, probability, and game theory. Volume 1 is rated 4.5/5 stars on 11 reviews. https://www.amazon.com/gp/product/1517421624/
“Math Puzzles Volume 2” is a sequel book with more great problems. https://www.amazon.com/gp/product/1517531624/
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“40 Paradoxes in Logic, Probability, and Game Theory” contains thought-provoking and counter-intuitive results. (rated 4.9/5 stars on 7 reviews) https://www.amazon.com/gp/product/1517319307/
“The Best Mental Math Tricks” teaches how you can look like a math genius by solving problems in your head (rated 4.7/5 stars on 3 reviews) https://www.amazon.com/gp/product/150779651X/
“Multiply Numbers By Drawing Lines” This book is a reference guide for my video that has over 1 million views on a geometric method to multiply numbers. (rated 5/5 stars on 1 review) https://www.amazon.com/gp/product/1500866148/