let

j = the age of Jason now

c = the age of Chris now

j : c = 9 : 5 cross multiply

5j = 9c

in 5 years, Chris age will be 4 more than half of Jason's age

c + 5 = 4 + (j/2)

by solving the system of equations

5j = 9c

c + 5 = 4 + (j+5)/2

we find

j = 27 years

c = 15 years

click here to see the step by step solution of the system of equations

Jason is 27 years old now.

Chris is 15 years old now.