The polygons are similar. Solve for x.
scale factor from A to B = 3:5

Answer:
9
Step-by-step explanation:
if scale factor is 3/5, then
(x+12):35=3:5, ⇒
[tex]\frac{x+12}{35} =\frac{3}{5}; x=21-12; x=9[/tex]