The first equation given is y = 3 - 1/2x In other words, y is the same as 3 - 1/2x. We can replace y in the second equation with 3 - 1/2x This is known as substitution (think of a substitute teacher who is a temporary replacement for your teacher)
Doing this leads to... 3x+4y = 1 3x+4*y = 1 3x+4*( y ) = 1 3x+4*( 3 - 1/2x ) = 1 <<--- y has been replaced with 3-1/2x 3x+4*(3) +4*(-1/2x) = 1 3x+12-2x = 1 3x-2x+12 = 1 x+12 = 1 x+12-12 = 1-12 <<-- subtracting 12 from both sides x = -11 Which is why the answer is choice C) -11
