a. We let x be the amount of money Trey initially had prior to mowing lawns. After moving lawns, Trey will have,
x + 40
Then, his parents double this amount such that his money will become,
2(x + 40)
This amount is equal to 234. Solving for x,
2(x + 40) = 234 ; x = 77
b. This approach is better than the usual arithmetic in that we just assigned a variable to a certain number and work on with the calculation without having to go through the long process of adding up everything before finally arriving to the final answer.
