Hey there!

Since the first number cant be zero there are only 9 options (1 thru 9), however for the next seven they can be zero, thus there are 10 options (0 thru 9). for the letters, the first option will be 5 as and the second will be 4 as there is no replacement. This gives:

\(9\times 10^7\times 5\times 4=1800000000\)

Thus there are 1.8billion possible student numbers

I could be wrong here but I do believe this is how you do it... Hope this helped :)