If the triangles are similar, then the sides are proportionate and the bases are as well. Set up the proportion like this, with side lengths on top and base lengths on bottom: 
. Cross multiply to get 4x = 60. That means that x = 20.
72 in expanded form thanks
2 answers:
You might be interested in
By the binomial theorem, the term in the expansion of
is
which suggests that the contribution of the binomial coefficient should make up the remaining factor of 21. That is,