Have been stuck on this problem for the past hour. can someone be so kind and explain it to me. I have a Quiz tomorrow on this. solving systems using substitution y = - 7y + 3; Y+ 7x = 10

Your starting equations are

y = -7y + 3 and
y + 7x = 10, is that correct? The previous response has an x in the first sentence, so I wanted to ask.

y = -7y + 3 simplified is
8y = 3
y = 3/8 (0.375 as a decimal)

If we sub 0.375 for y in the second equation, we can solve for x.

y + 7x = 10
0.375 + 7x = 10
7x = 9.625
x = 1.375

So y = 0.375 and x = 1.375

Checking the solution:
0.375 + 7(1.375)
= 0.375 + 9.625 = 10

and 0.375 = -7(0.375) + 3
0.375 = -2.625 + 3
0.375 = 0.375