This puzzle uses one of the simplest substitution ciphers. Each number represents the number in that position in the alphabet. It is fairly easy to create your own “cheat sheet” by writing out the alphabet and the numbers 1-26 next to each other, as shown:
Using this decryption tool, we find that each row spells out a number, namely:
Three
Eighteen
Twenty-five
Sixteen
Twenty
Fifteen
Twelve
Fifteen
Seven
Twenty-five
Writing each of these as numbers and repeating the process, we can see that that 3-18-25-16-20-15-12-15-7-25 decrypts to CRYPTOLOGY, a very appropriate answer for this puzzle.