To solve this problem, we should understand how order of operations works. Perhaps the best way to show you this would be solving the problem with all of the work clearly labeled?
=4[2(21-17)+3] Original Problem =4[2(4)+3] Solved the Parentheses =4[8+3] Multiplied the 2 and 4 =4[11] Added the 8 and 3 =44 Multiplied the 4 and 11
An easy way to remember this is PEMDAS, which is an acronym for Parentheses, Exponents, Multiplication/Division, and Addition/Subtraction. Although it will not apply in this scenario (because we have brackets), it will come in handy for many others like this.
Using all of the information above, we can conclude that this expression equals 4.