the sum of a number divided by 8 and 3 equals 6

"A Number" means an arbitrary variable, let's call it x.

x divide d by 8 is written as a quotient
x/8

The sum of x/8 and 3 means we add:
x/8 + 3

Finally, equals means we have an equation, so we set our expression above equal to 6
x/8 + 3 = 6