Answer:
Red paint needed = x = 17.5 ounces
Explanation:
Ratio of red to blue paint = 5 ounces : 6 ounces
If she has 21 ounces of blue paint, how much red paint will she need?
Ratio of red to blue paint = x ounces : 21 ounces
Equate the ratios
5 : 6 = x : 21
5/6 = x/21
Cross multiply
5*21 = 6*x
105 = 6x
x = 105/6
x = 17.5 ounces
Red paint needed = x = 17.5 ounces