product of a number and 10: 10n
Seven less than the product of a number and 10: 10n - 7
so
Seven less than the product of a number and 10 is 50:
10n - 7 = 50
----------------------------
if you need to find the number n then
10n - 7 = 50
10n = 57
n = 57/10
n = 5.7