Substitution method?

Question

i really need help with these problems

r=3s
r=10-4s

x=3y-4
2x-y=7

y=2x-5
x=2-4y

Answer 1

r=3s
r=10-4s

Since from the 1st equation, we know that r=3s, replace r from the 2nd equation with 3s
So r=10-4s is really
3s=10-4s
Move the 4s to the left side so we get 7s=10
s=10/7
_________________
x=3y-4
2x-y=7
Since from the 1st equation, we know that x=3y-4, replace x from the 2nd equation with x=3y-4
So 2x-y=7 is really
2(3y-4)-y=7
6y-8-y=7
5y-8=7
5y=15 --->y=3
_________________
y=2x-5
x=2-4y

Same thing: replace y in the 2nd equation with 2x-5, so we get
x=2-4(2x-5)
x=2-8x+20
9x=22
x=22/9

Answer 2

Since r=3s and r=10-4s that means 10-4s=3s which means s = 10/7.

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2x=6y-8
2x=7+y

6y-8 = 7+y
5y = 15
y = 3

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y=2x-5
x=2-4y

Use different method (would be easier).

x = 2 - 4(2x - 5)
x = 2 - 8x + 20
9x = 22
x = 22/9

Answer 3

The substitution method is simple
y=3x-4
x=y+3
y=3(y+3)-4, because x = y+3
and solve for y and use to get x

Answer 4

1.3s=10-4s
7s=10
s=10/7
r=3(10/7) = 30/7

2.2(3y-4)-y=7
6y-8-y=7
5y-8=7
5y=15
y=3
x=3*3-4=9-4=5

Can you do last one?