Can someone help me with a math question?

Question

A total of 644 tickets were sold for the school play. They were either adult tickets or student tickets. There were 56 fewer student tickets sold than adult tickets. How many adult tickets were sold?

Answer 1

Let

A = Number of adult tickets sold

S = Number of student tickets sold

Therefore:

A + S = 644

S = A - 56

Substitution: (Since S = A - 56, plug in A - 56 for the value of S in the first equation)

A + (A - 56) = 644

2A - 56 = 644

2A = 700

A = 350 adult tickets were sold