Brad runs a lap every 5 minutes and Ty runs a lap every 4 minutes. If they started at the same time, when will they get to the beginning of the lap at the same time?

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