This is a question on simultaneous equations where two variable are given with two or more relational equations. if she bought $10 worth of donuts and brownies, and each donut costs $1.25 and each brownie costs $2.50.
Then,
1.25d + 2.50b = 10 where d and b are the numbers of donuts and brownies purchased respectively.
if She bought twice as many donuts as brownies, then