Adult tickets cost $4 and children tickets cost $1. 285 tickets are sold. And $765 is collected. How many adult tickets were sold.?Use substitution...

In the question the need is to determine the number of adult and child tickets  tickets sold out. So one of the unknown  is x.

We presume  x number of tickets for sdults are sold. The child tickets is automatically must be 285-x.

The collection of revenue from x adult tickets =  number of tickets* rate of tickets = 4x

The collection of revenue from 285-x child tickets = number*rate = (285*x)*1 =285-x.

The total collection  = 4x+285-x algebraically.......(1)

The actual collection = $765..............................(2)

Therefore the required equation of the problem:

Algebraic collection as at (1)  = actual collection as at (2). So,

$(4x+285-x) = %765. Or

4x-x +285 = 765. Or

3x- 765 - 285 = 480. Or

3x = 480. Or

3x/3 = 480/3. So

x = 160  is the number of adult tickets sold.

285 - x = 285 - 160 = 125 is the number of child tickets sold.

Check: 160+125 = 285 and revenue $(160*4+125) =$ (640+125) = $765