P(X <= 160) = 1/2 tells you straight away that .

To get :

where (from inverse tables, correct to four decimal places).

Therefore .

The slightly more difficult question would have been if they'd given you P(X <= 200) = 0.9113 and P(X <= 140) = 1/4.

Then you'd need to solve the following simultaneous equations:

.... (1)

.... (2)

for and ......