Explanation:
because they are similar it means 2 main things :
1. the angles on both figures are the same.
2. there is one constant scaling factor that applies to all lines of a figure to create the lengths of the corresponding lines in the other figure.
so,
12 × f = 30
f = 30/12 = 5/2
this factor f has to apply now also to the side with 16 in.
therefore,
??? = 16 × 5/2 = 8 × 5 = 40 in