Let the amount of adult tickets Stacey sold be 'A', and the amount of child tickets be 'C'.
We know the prices of each ticket, and hiw much she brought in, so we know that:
7A + 4C = 378
However, we also know that A = 2C, as she sold twice as much adult tickets as child tickets. Therefore 2A = 4C, so 2A - 4C = 0
When you subtract the equations;
(7A+4C) + (2A-4C) = 378 - 0
So 9A is 378, and A is 42, so Stacey sold 42 adult tickets.
We know that she sold half as many child tickets, so she had to sell 21 child tickets.
Always double-check your answers:
(7x42) + (4x21)
= 294 + 84
= 378, which was the original amount
So she sold 42 adult tickets and 21 child tickets
Hope this helped
