Answer: a) 1977060966, b) 146581344.
Step-by-step explanation:
Since we have given that
There are 10 numbers,
There are 26 lower case letters,
There are 26 upper case letters,
Since the first 3 characters have to be digits and next 6 can be upper or lower.
So, a) repetitions are allowed:

b) repetitions are not allowed:

Hence, a) 1977060966, b) 146581344.
What do you need help with and what subject
Answer:1695.75
Step-by-step explanation:
We know that there are 7 days in a week. Since 57 people rent skates each day, we know that 57*7=399 skates are rented each week. Since one skate cost 4.25, we know that 399*4.25 is the cost, which is 1695.75. (If you are not allowed to use a calculator, you can do 400*4.25-4.25, to make it easier to compute)