Answer :
Line 3
since he added which is against the order of opreation rule he was supposed to multiply first then add
again what he was supposed to do is
Line 2:21+5+6(2)
Line 3:21+5+12
since he added which is against the order of opreation rule he was supposed to multiply first then add
again what he was supposed to do is
Line 2:21+5+6(2)
Line 3:21+5+12