AMC 10A 2020 Problem 24

Let n be the least positive integer greater than 1000 for which

\operatorname{gcd}(63, n+120)=21 \quad \text { and } \quad \operatorname{gcd}(n+63,120)=60

What is the sum of the digits of n ?

Answer Choices
A. 12
B. 15
C. 18
D. 21
E. 24