3r+b/a +y =w solve for r
would the answer be
r=wa-y-b/3
no.
Taking it as written,
3r+b/a+y = w
3r = w-y - b/a
3r = (wa-ya-b)/a
r = (wa-ya-b)/(3a)
If you meant
(3r+b)/a + y = w
(3r+b)/a = w-y
3r+b = aw-ay
r = (aw-ay-b)/3
Maybe if you use some parentheses things will be clearer.