Take into account that the Newton's second law is given by the following formula:
F = m·a
where:
F: force
m: mass
a: acceleration
when you solve the formula above for acceleration a, you obtain:
a = F/m
if the mass is quadruplied, you have:
a' = F/(4m) = 1/4 · F/m
a' = 1/4 · a
that is, the acceleation is reduced to one quarter of the initial acceleration.
