AMC 12 2024a Problem 5

A data set containing $20$ numbers, some of which are $6$, has mean $45$. When all the 6s are removed, the data set has mean $66$. How many 6s were in the original data set?

$\textbf{(A) }4 \textbf{(B) }5 \textbf{(C) }6 \textbf{(D) }7 \textbf{(E) }8$