Estimate then find the difference or sum

86+17

Estimation for addition: 86 rounds up to 90 and 17 rounds up to 20 so:

90 + 20 = 110

Estimation for subtraction is the same thing but with subtraction

90 - 20 = 70

Now for the exact answers:

86 + 17 = 103

86 - 17 = 69

Your answers are 110, 70, 103, and 69.