order of operations
do inner part first
7 + 2[9 - 2(4-1)] --> 7 + 2(9 - 2 * 3) (removed brackets and replaced with parenthesis, no internal parenthesis any longer)
do internal multiplication next (multiplication and division have higher priority than addition and subtraction)
7 + 2(9 - 2 * 3) --> 7 + 2(9 - 6)
do internal subtraction next
7 + 2(9 - 6) --> 7 + 2 * 3
do multiplication first
7 + 2 * 3 --> 7 + 6
do the addition
7 + 6 = 13
answered
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