Cross Training Questions - Can someone answer this question..9th grad algebra story problems, set up problem, find the 2 variables, solve

Can someone answer this question..9th grad algebra story problems, set up problem, find the 2 variables, solve

A store sold 28 pairs of cross trainer shoes for a total of $2220. Style A sold for $70 and Style B sold for $90. How many of each were sold?

a+b=28 70a+90b=2220 system of equations 13 pairs of B 15 pairs of A
Make equation 70x+90(28-x)=2220, where x denotes quantity of style A shoes. You get x=15. Hence, style B sold 28-15=13 pairs.