Nikki goes to the store to pick up boxes of highlighters and pens for her class. altogether, she buys 22 boxes. a box of highlighters costs $4 and a box of pens costs $2. in all, she spent $58 on highlighters and pens. determine if each equation is a part of the system of equations that can be used to find the number of each type of item that was sold. the variable x represents the number of boxes of highlighters, and y represents the number of boxes of pens.