Note: The main operation of the question is not visible. I'll assume it's 259 - 143.
Tran did right at expanding the numbers to operate, but when subtracting, he forgot to subtract 50 - 40 = 10 and 9 - 3 = 6. He added them instead.
That is why he got the wrong result.
Julio expanded the numbers correctly and subtracted each digit as he should. Consequently, he got the right answer 116.
Answers:
Who was right? How do you know?
Julio was right because he correctly subtracted and got an accurate result.
What did the other student do wrong? Why do you think that happened?
Tran added the last two digits (the ones and the tens) instead of subtracting them. He should have gotten distracted.