Answer:
19
Step-by-step explanation:
its just addition
This is a sum and difference problem, with the equations
R-N=35
R+N=635
The solution of which is
R=(635+35)/2=335
N=(635-35)/2=300
In general, the sum and difference problem can be solved (most of the time mentally) using
Larger number = (sum + difference)/2
Smaller number = (sum - difference)/2
We have 26 letters and 10 digits.
So, we have 26 choices for the first letter, 25 choices for the second letter (we can't pick the one we already chose), and 10 choices per digit (we can always choose any digit, because we can repeat them).
This leads to a total of

possible car targs.