Use 3.14 n for to estimate the area of a circle if the diameter is given on your answer to the nearest hundredth if necessary

Can someone me and do the problem plz so i can understand it more better

What adds to be the bottom number but also multiplies to be the top number with 8 on the bottom and 15 on top

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