Add: 13 and 15
13 and 15 13 + 15 = 28
Add: 13 and -15
Add: -13 and -15
Add: -528 and -243
Add: -623 and 326
Add: 257 and -254
Subtract: -5 from 8
Subtract: 4 from -7
Subtract: -8 from -2
Subtract: -3 from 12
Subtract: -123 from 453