Investigator smith is convinced that he has found a gun used in two shootings. when compared under the microscope, the two bullets do not seem to match up. if investigator smith is correct, what could be a reason why the bullets don't match?

the bullets hit at different speeds.

the bullets were bought from different gun stores.

the bullets were fired one right after the other.

one bullet was fired several years after the other.

D) One bullet was fired several years after the other.

Explanation:

Every gun barrel has rotating groves because gives to the bullet a spin movement in order to improve accuracy during its flight. This spiralling groves leave in the bullet some unique marks, that if you can fire another bullet from the same gun, under a microscope an investigator can match this groves. But time and the use on the gun can change the patron of this marks leading to the deterioration on the gun barrel, possibly take us to a missmatch on two bullets fired by the same gun.

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.

: -)