Write as a Common Fraction $4.2$ A) $\frac { 21 } { 50 }$

Write as a common fraction.
- $4.2$

A) $\frac { 21 } { 50 }$
B) $\frac { 6 } { 25 }$
C) $\frac { 21 } { 5 }$
D) $\frac { 12 } { 5 }$