Please help, I'll be giving brainliest. Prove that the rational numbers are closed under addition. Please let me know if I'm correct, and if not what the answer should be, I'll be giving brainliest.

In the given figure ar(adf) =ar(cda) and ar(cdf) = ar(cdf). show that abdc and cdfe are trapeziums.

Acomputer store buys a computer system at a cost of $370.80. the selling price was first at $ 618, but then the store advertised a 20 % markdown on the system. answer parts a and b. a. find the current sale price.

On which number line are -3 and its opposite shown