I know how its done!
Remember, PEMDAS
Do the exponent first.

Then you have to do Multiplication And division from left to right.
21/7=3
20*100=2000
2000*2=4000
3+4000-3
Last do Addition and subtraction from left to right.
3+4000=4003
4003-3=4000
Answer is 4000Hope that helps! And I hope I did it in time.