What is the value of the expression 9 x [ (21 - 4) - (2+7) ]

step 1.) do the problems in the parenthesis first then you would get ...

9 x [ (17) - (9) ]

step 2.) subtract what left inside the parenthesis 17-9 you should get 8.

step 3.) so your problem is now 9 x 8 and your answer is 72

9 x [ (21 - 4) - (2+7) ]

72 would be the answer you do the parenthesis first, 21-4 is 17, then 2+7 is 9 17 minus 9 is 8, 9 times 8 is 72.