Question 660494
x = ron's # of tickets
y = kathy's # of tickets

x + y = 20  :  rearrange as x = 20 - y
2x + 4.5y = 60
Substitute the first into the second equation
2(20-y) + 4.5y = 60
Distribute the 2
40 - 2y + 4.5y = 60
Combine like terms
40 + 2.5y = 60
40 - 40 + 2.5y = 60 - 40
2.5y = 20
2.5y/2.5 = 20 / 2.5
y = 8 tickets that Kathy sold
so,
x = 20 - 8 = 12 tickets that Ron sold
Proof
2(12) + 4.5(8) = 24 + 36 = 60