These equations can be used in solving distance-time-speed problems, age problems, geometry, mensuration and combinatorics problems. These problems can be solved by supposing any two variables X and Y. The values for these variables can be taken out by - 1. Finding their values in terms of each other. Exm- X + Y = 7. & X = 7 - Y. 2. Adding multiple equations. 3. Eliminating common terms.