(√3x+1) + 3 = x ? ...5a-2(√a+3) =2a-1

I do not understand these I keep getting the wrong answer please help and show work .
Thank you!

(√3x+1) + 3 = x
correct answer: x=8


5a-2(√a+3) =2a-1
correct answer:a=1

√(3x + 1) + 3 = x

√(3x + 1) = x - 3

3x + 1 = (x - 3)^2

3x + 1 = x^2 - 6x + 9

0 = x^2 - 9x + 8

0 = (x - 1)(x - 8)

x = {1, 8}

check for extraneous solutions

√(3*1 + 1) + 3 = 1
√4 + 3 = 1
2 + 3 = 1
5 = 1
1 is NOT a solution

√(3*8 + 1) + 3 = 8
√25 + 3 = 8
5 + 3 = 8
8 = 8

x = 8


5a - 2√(a + 3) = 2a - 1
-2√(a + 3) = -3a - 1
√(a + 3) = -(3a + 1) / -2
√(a + 3) = (3a + 1) / 2
a + 3 = (9a^2 + 6a + 1) / 4
4a + 12 = 9a^2 + 6a + 1
0 = 9a^2 + 2a - 11
0 = (9a + 11)(a - 1)
a = {-11/9, 1}

a = 1 will be the only solution