x = adult tickets and x+58 = student tickets
Create the equation from the problem.
x + x + 58 = 708
Combine like terms.
2x +58 = 708
Subtract 58.
2x = 650
Divide by 2.
x = 325
Therefore, your answer is:
there were 325 adult tickets sold.
(Adding 58 to that number will get you the student tickets sold which is 383 if they ask.)