As the exercise says, the triangles are similar. So, we can set up proportions between correspondent sides.
In order to solve for x we can set up the proportion between the horizontal and vertical sides:
Solving this proportion for x implies
Now you can solve for m and p using the pythagorean theorem, because both triangles are right:
Then, we know that the hypothenuse of the big triangle is m+p, so we have
which implies
Let the required no. be x
Then the equation is-
(150/100)x = 750
=> x = 750 × (100/150)
=> x = 500
Ans- 750 is 150 percent of 500.