Solve each of the following systems of equations. Find all solutions. (a) \begin{align*} x+y&=-1,\\ 3x &= 4-3y. \end{align*} (b) \begin{align*} 3x - 4y + 2&=0,\\ 10 - 10y& = 10y - 15x. \end{align*}
(a) (x,y) = (2,-4)
(b) (x,y) = (7/8, 3/8)