Simultaneous equations

Question

y = 12x + 420

y = 15x + 330

how do I solve the two simultaneous equations above using algebra?

Answer 1

12x+420= 15x+330

-12x -12x

________________

420 = 3x+ 330

-330 -330

________________

90= 3x divide the both side by 3 90/3 = 3x/3

result x=30

substitute x= 30 into one equatıon above you can choose either one

Pl

y=12x+420 y= 12(30)+420 y=360+420= 780

so result will be (30, 780)

Answer 2

subtract one equation from the other to get

-3x +90 = 0

x = 30

substitute that into either equation to solve for y

y = 780