5x+4y=6 and 7x-4y=-78

Question

I don't know what to write but I need to use substitution to solve this problem.

Answer 1

Substitution method

Given equations are 5x +4y  = 6

Subtract 5x  from each side.

4y  = -5x +6

Divide to each side by 4.

y = (-5x +6)/4 ---> (1)

And 7x -4y = -78 ---> (2)

From (1) substitute the y  value in (2).

7x -4(-5x +6)/4 = -78

7x+5x-6 = -78

12x -6 = -78

Add 6 to each side.

12x  = -72

Divide to each sid by 12.

x  = -6

Substitute the x  value in (1).

-30+4y  = 6

Add 30 to each side.

4y  = 36

Divide to each side by 4.

y  = 9

Solution x  = -6 and y  = 9.