Becky wants to paint the walls in her bedroom. A gallon of paint will cover $400 \mathrm{ft}^{2}$. She measures the surface to be painted; it's 76,320 in ${ }^{2}$. How many gallons of paint should she buy? She should buy whole gallon(s).

Step 1 ：First, we need to convert the area from square inches to square feet because the coverage of the paint is given in square feet. There are 144 square inches in a square foot. So, we divide the total area in square inches by 144 to get the area in square feet. The calculation is \(\frac{76320}{144} = 530\) square feet.

Step 2 ：Then, we divide the total area in square feet by the coverage of the paint to get the number of gallons needed. The calculation is \(\frac{530}{400} = 1.325\) gallons.

Step 3 ：Since Becky can only buy whole gallons, we will round up to the nearest whole number if necessary. So, Becky needs 2 gallons of paint.

Step 4 ：Final Answer: Becky should buy \(\boxed{2}\) gallons of paint.