Joe had one medium fries and two small sodas for 620 calories on Monday, and two medium fries and one small soda for 820 calories on Tuesday. How many calories are in one order of fries and one soda?

1. Let f be the calories in one order of fries and s be the calories in one soda, giving the system f + 2s = 620 and 2f + s = 820. 2. Multiply the first equation by -2 to make the f-coefficients opposites: -2f minus 4s equals -1240. 3. Add this to the second equation: -3s equals -420, so s equals 140. 4. Substitute s = 140 into f + 2s = 620 to get f equals 340, so fries have 340 calories and soda has 140 calories. _Source: OpenStax Elementary Algebra (CC BY 4.0), Ch 5 "Systems of Linear Equations", section 5.3 Solve Systems of Equations by Elimination_