I am lost. I don't know how to solve this. 3+√x^2-8x=0?

Answer 1

3 + x - 8x = 0
3 = 7x
x = 3/7

However you MAY have meant:-
3 + √(x² - 8x) = 0
√(x² - 8x) = - 3
x² - 8x = 9
x² - 8x - 9 = 0
(x - 9)(x + 1) = 0
x = 9 , x = - 1

Conclusion
MUST USE BRACKETS!!!

Answer 2

is x^2 -8x under the radical sign?

If it's not, then:
3 + sqrt(x^2) - 8x = 0
3 + x - 8x = 0 : taking square root
3 - 7x = 0 : combining x
x = 3/7 : solve for x

If it is, then
3 + sqrt(x^2 - 8x) = 0
sqrt(x^2 - 8x) = -3 : bring 3 over
sqrt(x^2 - 8x)^2 = (-3)^2 : square both sides
x^2 - 8x = 9
x^2 - 8x - 9 = 0
x = ? : use quadratic formula