x= amount he has saved
x+40 +(x+40)=234
x= saved amount plus 40 he saved mowing lawns plus the amount his parents give him is 234
2x+80 = 234
subtract 80 from both sides
2x = 154
divide each side by 2
x=77
he had 77 saved before he mowed lawns
b) I am not sure what they mean. I am thinking you would have to guess a starting value for trey and calculate and see if you got the right answer. kind of like quess and check. you would need to do this many times before you got the right answer