The activity pictured is called goat tying.
Let rs.5 denominations be x , then rs 10 denominations will be 90-x
then total amount 5x + 10(90-x) which is rs.500
5x + 10(90-x) = 500
900 - 5x = 500
400 = 5x
therefore x = 80
therefore no. of rs.5 is 80
no. of rs.10 is 90-x = 90-80 = 10
Part A: Kennedy's expression is incorrect because 0.07 is 7 percent, not 70.
Part B: The correct expression would be 0.7 * 20, which equals 14
First, you'll use the "Log power rule," which says that

. In this case, you're going from the form on the right (with p in front of the log) to the form on the left (with p in the exponent position). So, the expression becomes:

Then, you'll use the "Log product rule," which says that

. Again, you're going from the form on the right to the form on the left (basically, from the sum of the logs, to a log of the products). So you get:

There's your expression simplified into a simple logarithm.