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)
