How do you solve st+3t=6

You will factor out the common factor of t if you are solving for t. you will then divide both sides by (s+3) to make t the subject of the formula. for this question you can only get t in terms of s.
so:
st+3t=6
t(s+3)/(s+3)=6/(s+3)
t=6/(s+3)

if you are required to solve for s then you are going to subtract 3t from both sides. you can factorise 6-3t .you will then divide both sides by t to isolate s.for this question you can only get s in terms of t.so:

st+3t-3t=6-3t
st/t=2(3-t)/t
s=2(3-t)/t

The answer of the question is x=0 and y=