Hello from MrBillDoesMath!
Answer:
Problem 1: x = 7/10, y = 21/5
Problem 2: x = 10, y = 30
Discussion:
Problem 1: Substitute (y = 6x) in (4x + y = 7 ) to get
"4x + y = 7"
4x + (6x) = 7 =>
10x = 7 =>
x = 7/10
As y = 6x, y = 6(7/10) = 42/10 = 21/5 = 4 1/5
Problem 2:
Substitute (y = 3x) in (x = -2y + 70 ) to get
"x = -2y + 70"
x = -2(3x) + 70 =>
x = -6x + 70 => add 6x to each side
x + 6x = -6x + 6x + 70 =>
7x = 70 =>
x = 70/7 = 10 =>
y = 3x = 3(10) = 30
Thank you,
MrB