Remark
All you need do is assume the small triangle is similar to the large one. MO:ML :: MP:MN must be solved.
Givens
MO = 28
ML = 28 + 14
MP = y
MN = y + 18
Equation
28:28+14 :: y: y + 18
Solve
28/42 = y / (y + 18)
28*(y + 18) = 42y Remove the brackets
28y + 18*28 = 42y
28y + 504 = 42y Subtract 28y from both sides.
504 = 42y - 28y
504 = 14y Divide by 14
504/14 = y
y = 36
