The force between 2 charged objects is given by, F = kq1q2/d².
where k ⇒ constant
d ⇒ distant between the 2 objects.
In this case, k and d are constants.
So, let k/d² = x
since q1=q2,
F = xq²
x = F/q²
After replacing q1 with 4q, the new force on +q will be:
F = xq.4q
= Fq4q/q²
= 4F
The new charge on +q is 4F.