Answer:
7.5
Step-by-step explanation:
Triangles: RST and RPQ are similar so
Triangle RST has 12.5 and x
Triangle RPQ has 20 (comes from 12.5+7.5) and x+4.5
Therefore you divide
x/x+4.5 = 12.5/20
20x= 12.5x+56.25
7.5x=56.25
x=7.5
