let c represent cookies, m represent muffins. set up a system of equations:
2c+3m=16
m=2c
(the top equation shows that cookies are $2 each, and muffins are $3, and that the total cost is $16. the bottom equation shows that Lori bought twice as many muffins as cookies).
then solve the system of equations by substitution, substituting 2c for m in the top equation: