start by calculating the acceleration using the third equation of motion
v2=u2+2as
from rest u=0
22=02+2(a)(3)
4=6a,a=0.67m/s2
now a=mFnet=mmg−frictionforce
ma=mg−frictionforce
frictionforce=ma−mg=30×0.67−30×10=−279.9N
so the average friction force which is acting in the opposite direction is 279.9N
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