Solution:
Given that,
Melanie's bedroom walls are painted 45% painted
The area of her walls totals 420 square feet
To find: number of square feet of Melanie's walls still need to be painted
From given,
45 % of wall is painted
Which means, 100 % - 45 % = 55 % is still remaining to be painted
55 % of total area is still remaining to be painted
Therefore,
Remaining to be painted = 55 % of 420
[tex]\text{ Remaining to be painted } = \frac{55}{100} \times 420\\\\\text{ Remaining to be painted } = 0.55 \times 420\\\\\text{ Remaining to be painted } = 231[/tex]
Thus 231 square feet of Melanie's walls still need to be painted