Let y= 15-2X, and the original formula can be transformed into:

y(5+y)= 150

y^2+5y- 150=0

(y+ 15)(y- 10)=0

The solution is:

Y=- 15 or y= 10.

Y= 15-2X

X= 15 or x=5/2, x = 2.5m