SureMath - the math software for 21st
solving - was used to solve this problem.
Downlo ad SureMath file.
Word problems encountered in early grades can be usually be solved by the givens-based approach.
As grade level advances this is no longer reliable. Problems of any substance require a concept-based (knowledge-based) approach.
The change from givens-based problems solving to concept-based problem solving requires practice. It is much like changing from hunt and peck typing to touch typing. Both changes require considerable effort but the rewards are substantial.
The problem solution was developed by Howard C. McAllister using SureMath.