Answer:
400,000,000 tons
Explanation:
You could reword this sentence to ask the question, "100,000,000 is 25% of how much?"
The word "is" means equals, the percent will be .25 in decimal form, the word "of" means to multiply, and "how much" is x, our unknown. In equation form, then, this looks like
100,000,000 = .25 × x
We will divide both sides by .25 to get that
x = 400,000,000
That's how much grain was grown in 2008