The task is to generate the correct answer for a given math problem.

Problem: when positive integer n is divided by 5 , the remainder is 1 . when n is divided by 7 , the remainder is 3 . what is the smallest positive integer k such that k + n is a multiple of 40 .
7

Problem: a cistern 5 m long and 4 m wide contains water up to a depth of 1 m 25 cm . the total area of the wet surface is :
42.5 m 2

Problem: the largest three digit number which is a perfect cube , is :
72