Using the order of the letters in the triangles find the corresponding sides:
BL is similar to JF
LT is similar to KF
BT is similar to JK
Find the scale between LT and KF
9/12 = 3/4
The smaller triangle is 3/4 the size of the lager one.
This means BT = 3/4(JK) = 3/4(4) = 3
So x = 3, so side BL = 2x = 2(3) = 6
Now to solve for y:
BL is 3/4(JF)
6 = 3/4(y)
Solve for y by dividing both sides by 3/4
Y = 6/(3/4)
Y = 8
X = 3, y = 8