Use the cube of a binomial representing a sum to calculate 13^3

Jack did 3/5 of all problems on his weekend homework before sunday. on sunday he solved 1/3 of what was left and the last 4 problems. how many problems were assigned for the weekend?

Campus rentals rents 2 and 3 bedrooms apartments for $700 ans $900 a month respectively. last month they had six vacant apartments and reported $4600 in lost rent. how many of each type of apartment were vacant?

If a is a nonzero real number then the reciprocal of a is