Please help and explain how to do it

So F(m) because F dollars for every mph over the speed limit
so 40 dollar speeding fine so +40 
10 dollars for every mile over and m=miles over so put them all toghether and get
F(m)=10m+40

1.
so if you were going 78 mph
to find the mph over you would do 78-70=8mph over so put in 8 for m and get
F(8)=10(8)+40=80+40=$120 fine for going at 78 mph

Idont knowgfdhdhfhggg.

Provide an equation