Let
x -----> Karen's age now
y ----> Oliver's age now
we have that
x=y+21 --------> equation 1
(x+4)=2(y+4) ---> equation 2
Solve the system of equations
Substitute equation 1 in equation 2
(y+21+4)=2(y+4)
solve for y
y+25=2y+8
2y-y=25-8
y=17
Find out the value of x
x=17+21
x=38
therefore
Karen is 38 years old now
Oliver is 17 years old now
