M = 7.3 * pi ≈ 22.934
How I got there: this is a rather simple algebraic problem, steps to solve:
1. Isolate variable, multiplay pi on both sides: M / pi * pi = 7.3 * pi
2. pi on left side cancels, so you get: M = 7.3 * pi
3. Solve! The answer is around 22.934
