7 x 90 = 80 x 100 =

$$7 \times 90$$

Multiply 7 by 9 to get 63, then add the zero from 90.

$$7 \times 90 = 630$$

$$80 \times 100$$

Multiply 8 by 1 to get 8. Then count the total number of zeros in both numbers (80 has one zero, 100 has two zeros, for a total of three zeros) and append them to 8.

$$80 \times 100 = 8000$$

The solutions are:
$7 \times 90 = \boxed{\text{630}}$
$80 \times 100 = \boxed{\text{8000}}$