The some of the numbers is 77. The greater number is 5 more than the smaller number. Which equation can be used to solve for the smaller number?

Let the smaller number be x and the larger one be y

x + y = 77

y = x + 5

Substituting into the first equation

x + (x + 5) = 77

2x + 5 = 77

Subtracting 5 to both sides

2x + 5 - 5 = 77-5

2x = 72

Divide both sides by 2

2x/2 = 72/2

x = 36