An easy one in dynamics.

for the first one

net force on M due tension =0 as they cansel out
let frction on m be f backwards

first we will consider friction is static and see i.e. both have the same acceleration

we get

F-f/m=f/M

80-f/10=f/15
80-f/2=f/3

f=240/5=48

hence acceleration=

F-f/m=80-48/10=3.2

in the second case observe a froce F is acting on pully net bacwarkds due to tension

let friction act backwards on m

then

attempting to keep ststic friction

f-F/M=F-f/M

thus F=f=80 but maximum f=μN=60

so here maximum friction i.e. 60 will act

thus acceleration = 80-60/10=2

second answer will be 1.4 m/s²

by the slab you mean which one??

if the M then only it will be 1.4

sorry you probably worked out the acceleration of m (I thought it was for M). The slab is the bigger mass.