Answer: 4 * (12.75 + x) = 61
Explanation:
Each of the 4 friends paid $12.75 so that is:
= 4 * 12.75
Assuming the tip is denoted as x it would be:
= 4x
Putting them together is:
4 * (12.75 + x) = 61
Solving the equation would give:
4 * (12.75 + x) = 61
51 + 4x = 61
4x = 61 - 51
x = 10/4
x = $2.50