21-3c if c=7

how did you get 7 for a answer

21-21 = 0

21-3c if c=7

{substitute and solve}.
so...
21-3x7
21-21
=0

To solve the expression 21-3c, where c = 7, we can substitute the value of c into the expression and then perform the calculation.

Step 1: Replace c with 7 in the expression.
21 - 3(7)

Step 2: Perform the multiplication first.
21 - 3 * 7

Step 3: Calculate the multiplication.
21 - 21

Step 4: Perform the subtraction.
0

Therefore, the value of 21 - 3c, where c = 7, is 0.