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she used 6.525 pints of white paint.

Step-by-step explanation:

Kelly uses 8.7 paints of blue paint and white paint to paint her bedroom walls. If 1/4 of this amount is blue paint, it means that the amount of blue paint that she used in painting her bedroom walls is

1/4 × 8.7 = 2.175 pints of blue paint.

Since the rest of the paint is white, it means that the pints of white paint that she used to paint her bedroom walls is

8.7 - 2.175 = 6.525 pints of white paint