The two-digit numbers that can be formed using the digits 4 and 5 (allowing repetition as implied by 'from 4 & 5') are 44, 45, 54, and 55. Their sum is 44 + 45 + 54 + 55 = 198. If repetition is not allowed, the sum is 45 + 54 = 99. The stored answer assumes no repetition.