Solve system of equations

At McDonalds, a packet of ranch dressing has 10 more calories than eight side salads. Three side salads and two packets of ranch dressing have a total of 400 calories. How many calories are in each item?

R = 8S + 10

3S + 2R = 400

Substitute first formula into second formula

3S + 2 (8S + 10) = 400

3S + 16S + 20 = 400

19S + 20 = 400

19S + 20 - 20 = 400 - 20

19S = 380

19S / 19 = 380/19

S = 20

Plug 20 into first formula

R = 8 (20) + 10

R = 160+10

R = 170

Side Salads are 20 calories and Ranch Dressing is 170 calories.