What number adds 10 and multiplies 21

The numbers are 7 and 3.

7 + 3 = 10

7 x 3 = 21

It is easier to factor 21 than to find the addends of 10.

1, 3, 7, 21 - are factors of 21

1, 2, 3, 4, 5, 6, 7, 8, 9 - are addends of 10. Which is more numbers to consider than the factors of 21.

7 and 3. 7+3=10 and 7x3=21