HELP ME WITH THE FOLLOWING QUESTION
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Let f(x), x>0 be a non negative continous function and let F(x)=

f(t) d(t), x>=0.
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If for some c>0, f(x)<=c*F(x) for all x>=0 then
(a) f(x)=0 for all x>=0
(b) f(x)=x for all x>=0
(c) f(x)=x*x for all x>=0
(d) f(x)=1+x*x for all x>=0