Which set is of whole numbers but not natural numbers?

Which equation results from adding the equations in this system? x+6y=9 and -x+2y=-15

Suppose a laboratory has a 30 g sample of polonium-210. the half-life of polonium-210 is about 138 days how many half-lives of polonium-210 occur in 1104 days? how much polonium is in the sample 1104 days later? 9; 0.06 g 8; 0.12 g 8; 2,070 g

What is the probably of getting heads when poing a coin and getting a number greater than or equal to 5 when rolling a single diea) 1/6b) 1/3c) 1/4d) 1/12