Answer: 315 minutes.
Explanation:
To solve this, we need to find out how long it takes to make one bracelet first.
If it takes 45 minutes to make 3 bracelets, we need to divide 45 by 3, which gives us 15.
This means it takes 15 minutes to make one bracelet.
Now, we need to multiply 15 by 21.
15 x 21 = 315.
This means it will take 315 minutes to make 21 bracelets.