There are four of each.
The number is 23.
Their sum is 41.
Sum
67
The 3 largest 2 digit prime numbers are 83, 89, and 97. The sum is 269
16
995
17, 53, 71
31
16
For the tens digit to be a prime number then it must equal 2, 3, 5 or 7. There are four 3-digit prime numbers that fit the above condition and also have the tens and units digits forming a 2-digit prime number. 131, 137, 173, 179. The person supplying the question may like to sum the various combinations.