The number of potatoes, p, is four more than half the number of green beans, g. which expression represents the number of potatoes in terms of the number of green beans?

Start by writing down "p" to be potatoes, set that equal to something like this: 
p=
now the "four more" part means addition, so on the other side of the equation write:
p=4+
now for the "half the number of green beans" means division by two (or multiplication by 1/2)
p=4+g/2 OR p=4+1/2(g)
now convert the equation to be in terms of g by subtracting 4 from both sides and multiplying both sides by 2 (or dividing by 1/2)
g=2(4-p) or g=(4-p)/(1/2)