16[(4.2×3.5)-9.5] how to solve this problem

It's order of operations (PEMDAS)
Solve parenthesis first, then exponents, them multiplication and/or division, and finally addition and or subtraction.

So for this problem:

First, 4.2 X 3.5 is 14.7
Now you have 16[14.7 - 9.5]

Next you still have parenthesis, or in this case, brackets. So 14.7 - 9.5 is 5.2.

Finally, multiply 16 by 5.2
Your answer is 83.2