An auto mechanic ordered eight car spark plugs and four truck spark plugs. car spark plugs cost $.75, and truck spark plugs cost $3.00 apiece. use the distributive property to find the total cost of these parts.

The first thing we should know is the definition of commutative property.
 Commutative property:
 The distributive property of multiplication over addition in elementary algebra is that in which the result of a number multiplied by the sum of two or more addends is equal to the sum of the products of each summand by that number. In algebraic terms we have then:
 4 * ((2 * 0.75) + (3)) = (8 * 0.75) + (4 * 3) = 6 + 12 = 18 $
 
 the total cost of these parts is $ 18