We need to turn this phrase into an algebraic equation and then solve...
in math
"of" means times (x)
"is" means equals (=)
"sum" means you're going to add
The sum (we are going to add) of 15 and six times a number t (15 + 6t) is 81 (= 81). So write it out...
15 + 6t = 81
Now solve for t. First subtract 15 from each side...
15 + 6t - 15 = 81 - 15
6t = 66
Now divide each side by 6 to get t by itself...
6t/6 = 66/6
t = 11
Done!
