At west middle school, students are asked to pick their lunch ahead of time so the kitchen staff will know exactly what to prepare. on monday, 6 times as many students chose hamburgers as chose salads. the number of students who chose pasta was was 20 more than the number of students who chose pasta. if 280 students bought lunch, how many students ordered salad?

In your question you wrote that those who chose pasta were 20 more than chose pasta so I'll assume you meant "than chose hamburgers"... That said, if you let salad = X then ha.burgers = 6x and pasta = 6x + 20

If we add them together we will get the total orders of 280, so our equation is

x + 6x + (6x + 20) = 280
13x + 20 = 280
13x = 260
x = 20

Remember x = salad so 20 people ordered salad

just for your info...

hamburgers would be 6x or 6 × 20 = 120 and

pasta would be 6x + 20 or 6×20 +20 = 140