Answer :
Thank you for posting your question here at brainly. The answer to the above question is the first one in the choices which is 15. Below is the solution:
3x + 10 = 55
Subtract 10 from each side...
3x = 45
Divide by 3...
x = 15
3x + 10 = 55
Subtract 10 from each side...
3x = 45
Divide by 3...
x = 15