D because for x+6 to be even, x must be even. So, a is incorrect because an even - an odd is not even and neither are b and c because of the same logic. However, when you multiply an even by a whole number, you get an even. And when you add an even number to that it is still even so D would be the answer.
If Jeff has 5 grasshoppers, then he would have 15 crickets because x(grasshoppers)+10=y(crickets), and y(crickets)+5=z(ladybugs), which would leave Jeff with 20 ladybugs.
