Tickets to a school basketball game cost $4 for students and $7 for adults. At the end of the night, 168 tickets are sold for a total of $861. How many tickets are sold

4s+7a=861

s+a=168

This can be solved using either elimination or substitution. I am going to use substitution.

Solve s+a=168 for s

s=168-a

Replace 168-a for s in 4s+7a=861

4 (168-a) + 7a=861

672-4a+7a=861

Solve for a

672+3a=861

3a=189

a=63

Substitute 63 for a in s=168-a

s=168-63=105

So, s=105 student tickets and a=63 adult tickets