Answer is 55
Two ways you can approach this first you can subtract the three from the 10 and get 7. Square that to get 49. Now you know that x-6 has to equal 49 and the only option greater than 49 is 55
Second you can just take the problem step by step.
Subtract three from both sides.
Sqrt x-6 =7
Square both sides
X-6=7^2
x-6=49
Add six to each side
X=55