I’ll assume the c is b. (1/2) x (5) x (2) x (2) is 10
There rate is 1.67 or 1.66 repeated a day
The product of the greatest common divisor and the least common multiple of two numbers is always the product of the two numbers. So, you have

The answer should be obtuse. I'm not sure why it is saying it's incorrect but none of the other answers make sense.