Question 666558
adults  --------- x
children ----------- y

x+y = 280.........................(1)

Receipts = 140*100= 14000 cents

60x+25y=14000.....................(2)

Multiply equation (1) by -60

-60x-60y=-16800

add with (2)
-35y= -2800
y= -2800/-35
y = 80 the number of children