F-net = 0 = F - friction

friction = µ * N <-- normal force

The normal force is just the weight (since it's a flat surface):

friction = .12 * 6 * 9.8 = 7.056 N

Therefore the force must exactly balance that:

0 = F - 7.056
--> solve for F

F = 7.056 N

b) Same thing, only now there is an acceleration:

F = ma
-->

F-net = F - 7.056 = m * a

You know everything but F, in this case:

F - 7.056 = 6 * .18
-->
F = 1.08 + 7.056 = 8.136 N

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