Let A be the weight of the ant and C be the weight of the cargo, then since "An ant and its cargo weigh 76 milligrams" then we have the following equation
A+C=76
And from "The cargo is 18 times heavier than the ant. " we have this other equation:
C=18A
then we can replace the second equation in the first one
[tex]A+18A=76[/tex][tex]19A=76\text{ }[/tex][tex]A=\frac{76}{19}=4[/tex]Now, replacing A by 4 in the secon equation, we obtain
[tex]C=18(4)=72[/tex]Therefore, the answer will be that the Ant weights 4 miligrams and the cargo Weights 72 miligrams.