The small arcs inside the triangle show that they are similar, so first find the ratio between the similar sides that both have given lengths.
JK is 25, and MN is 30.
30/25 = 1.2
This means the larger triangle is 1.2 times the size of the smaller one.
So MP needs to equal 1.2 x the length of JL:
JL = 20
20 * 1.2 = 24
Now you have 4x-4 = 24
Now silve for x:
Add 4 to each side:
4x = 28
Divide both sides by 4:
x = 28 / 4
x = 7
