In the last two years, mari grew 2 1/4 inches, kim grew 2.4 inches, and kate grew 2 1/8 inches. write the amounts they grew in order from least to greatest

First, let's turn the fractions into decimal form so you can see the answer, more clearly. 
2 = 2.25
2.4 = 2.4
2 = 2.125

Now, after looking at the decimals, we can see which decimals are the biggest. They would order, from least to greatest, like this. 
1)  2.4
2) 2.25
3) 2.125

I hope this helps!