Solve the Problem $$\frac { 3 } { 4 }$$ As Many Vibrations as in the Previous Second

Multiple Choice

Solve the problem.
-After being struck with a hammer, a gong vibrates 21 vibrations in the first second and in each second thereafter makes $$\frac { 3 } { 4 }$$ as many vibrations as in the previous second. Find how many vibrations the gong makes before it stops vibrating.

A) 94 vibrations
B) 28 vibrations
C) 23 vibrations
D) 84 vibrations