Decoding Fun

So I got this code at school for fun and solved it in around 30m, give or take 10m, and I wanted to post in on here for fun to see if you guys could decode it!

UXKI JCBL PBXCOF WL KOF UXKI JCBL PBSTGB WL KGB ICOV HKIIBGL MTHDKGBF IT UXKI JCBL UCIXCO WL.

-TJCYBG UBOFBJJ XTJHBL

Hints:

Spoiler: Hint 1

count all the times an individual letter appears in the code, then match the 2 most appeared letters with the 2 most common letters used in the English alphabet

Spoiler: Hint 2

e is the most common letter used in the English alphabet, and T is the second

Spoiler: Hint 3

U=W