can someone please tell me if I got these right?

the serial # on a new $20 bill consists of 2 letters followed by 8 #'s and then a letter. how many different serial # are possible given the following conditions?
a. letters and digits can't be repeated.
26x25x9x8x7x6x5x4x3x2x24= 5,660,928,000

b. letters and digits can be repeated
26^3x10^8= 1.7576E12 (my teacher doesn't want it written that way) 1.7576x10^12

c. the first and last letters are repeatable vowels, the second letter is a consonant, and the digits can be repeated.
i got vowels-5 consonants-21
5x21x10^8x5= 5.25x10^10

Question

can someone please tell me if I got these right?

the serial # on a new $20 bill consists of 2 letters followed by 8 #'s and then a letter. how many different serial # are possible given the following conditions? 
a. letters and digits can't be repeated. 
26x25x9x8x7x6x5x4x3x2x24= 5,660,928,000

b. letters and digits can be repeated
26^3x10^8= 1.7576E12 (my teacher doesn't want it written that way) 1.7576x10^12 

c. the first and last letters are repeatable vowels, the second letter is a consonant, and the digits can be repeated. 
i got vowels-5 consonants-21
5x21x10^8x5= 5.25x10^10

phi · Answer

if by 8 #'s they mean 8 digits, there are 10 different digits 0,1,2...9

so the first one should start with 26x25x10...

phi · Answer

c. is probably correct, but sometimes "y" is a vowel   scythe, by...  and sometimes a consonant:    youth, yikes, ...
so if they are being tricky....

anonymous · Answer

ohh ok thank you for your help! yeah with c they might be tricking me!