270 tickets were sold at a school event. The total money collected is $1700, if the adults cost $10 and the student section cost $5. How many adult tickets were sold?

Question

My teacher gave this to us but he didn't explain it how. Can you help me answer this question and show the equation?

Answer 1

10 a + 5 s = 1700
so
s = 340 - 2 a

s+a = 270
340 - 2a + a = 270

a = 340-270

a = 70