An adult blue whale can eat 4.0 x 10^7 krill in a day. at that rate, how many can an adult blue whale eat in 3.6t x 10^2 days

3.65x10^2 is 3.65*100 and is equal to 365. 4.0*10^7 is simply adding 7 zeroes to the end of 4. So its 40 million simply. I hope that makes sense and that all you have to do is multiply. The reason they use scientific notation mostly is for significant figures but that's something else.

So, to reword the question, if a blue whale eats 40 million krill a day then how many will it eat in 365 days/a year? 
40*365=14600 million krill a year. Add six zeroes to get the number only version. 14 600 000 000 krill. Hope this helps!