A $4\mathrm{.}50-kg$ block is placed on top of a $12\mathrm{.}0-kg$ block that rests on a frictionless table. The coefficient of static friction between the two blocks is $0\mathrm{.}650.$ What is the maximum horizontal force that can be applied before the $4\mathrm{.}50-kg$ block begins to slip relative to the $12\mathrm{.}0-kg$ block, if the force is applied to each of the following?

$($a$)$ the more massive block

N

$($b$)$ the less massive block

N