Use substitution to solve the system

Question

3x+4y=-8, y=2x +9

Answer 1

do what the instructions say. you know that y can be expressed in terms of x, so SUBSTITUTE 2x+9 in place of y in the first equation.

 

3x + 4(2x+9) = -8.  Distribute, collect like terms, solve for x. Then back-substitute to compute y. EASY. Just like the examples in your textbook or notes!