If you round 18.77 with the correct significant figures? what is the answer?

Atotal of 766 tickets were sold for the school play. they were either adult tickets or student tickets. there were 66 more student tickets sold than adult tickets. how many adult tickets were sold?

What is the value of x in the equation7x+2y=48 when y=3

Hi i’m not sure how to do question 20 if u could explain how to do it that’d b great