Hello!
Let's do this step by step!
We must convert 24/40 to a decimal before we can find out what percentage of 40 is 24. 
To convert 24/40 to a decimal, we must multiply the numerator (24) by the denominator (40): 
24 ÷ 40 = 0.6
Now that we have the decimal form, we will multiply the decimal by 100 to convert it to a percentage. 
0.6 × 100 = 60
24/40 = 60% 
A N S W E R
60% of a lawn is planted with Kentucky blue grass.