Hello there! (-17) - 21 = -38.
When subtracting a negative from a negative, we can use the inverse operation to solve:
17 + 21 = 38
The sum will always take the sign of the greater number. Subtracting a negative from a negative is the equivalent of adding the two integers and possessing the sign of the greater number. We call this ‘Inverse Operations,’ and this is widely used throughout mathematical and algebraic expressions/equations. If you need extra help, let me know and I will gladly assist you.