C) are used to add the minerals in soil.​

Mix a thick, nutrient-rich compost into your soil to a depth of about 10 to 12 inches. Use a tiller or shovel for the task. Compost adds several macronutrients and micronutrients to soil, along with several trace minerals. It also can aid in making certain trace minerals more available to plants.

this should be the answer tell me if it is blank again

try using substitution:

x + y - 6 = x - y. (i'm not giving you the exact answer). since 0 = x - y, then sub 0 in the equation with x - y. combine your like terms, and then use inverse operations, and you'll have your answer.

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substitution is the answer in this case