Question

A key code must contain 2 letters and 3 numbers

Answer 1

26 letters {A; B; C; D;...;Z}

10 numbers {0; 1; 2; 3;...;9}

L-letter; N-number

code
LLNN
LNLN
LNNL
NNLL
NLNL
NLLN

26 · 26 · 10 · 10 · 6 = 135,200

Answer 2

26 choices for each letter, 10 for each number, do 26×26×10×10×10