Answer:
After 16 years Mr. Jibril will be twice as old as his son.
Explanation:
t - age Mr. Jibril
s - son age
t=4s (father is 4 times older than son)
t-4=7(s-4) (4 years ago they both have 4 year old less and father was 7 times older than son)
t=7s-28+4
t=7s-24
7s-24=4s
3s=24
s=8
t=32
x- years after Mr. Jibril will be twice as old as his son.
32+x=2(8+x)
32+x=16+2x
16=x
x=16