Melanie’s bedroom walls are 45% painted. the area of her walls totals 420 square feet. what is the number of square feet of melanie’s walls that still need to be painted?

She still needs to paint 231 square feet.
You can get that by find out what 45% of 420 is (420 x 45 = y, divide it by 100), and subtracting it from 420 (420 - 189 = 231).
Or you can go right ahead and calculate what is the remaining percentage, which is 55%, so (420 x 55 = y, divide it by 100).

The answer is 231 square feet. 45% is .45 in decimal form. You would multiply .45 by 420 and get 189. Then you would subtract 189 from 420 and get 231.

Ok you ask" Can the volume of a square or rectangle can be found by multiplying length by width?"
 The answer is YES you can . :)