Afarmer needs to mix 12 ounces of fertilizer for every 10 pounds of soil. how many pounds of fertilizer will the farmer need to make a mix that contains 120 pounds of soil?

12 ounces of fertilizer for every 10 pounds.  

How many pounds of fertilizer will the farmer need to make a mix that  contains 120 pounds of soil?

120 ÷ 10 = 12
12 × 12 = 144
When 12 ounces of fertilizer for every 10 pounds, when 120 pounds, you will need 144 ounces of fertilizer. 

Convert from ounces to pound:

1 ounce =  0.0625 pounds
0.0625 ×144 = 9
144 ounces = 9 pounds

The farmer will need 9 pounds (144 ounces) of fertilizer to mix 120 pounds of soil.