help me with this question

[tex]\\ \bull\tt\dashrightarrow Diameter=2(Radius)[/tex]
[tex]\\ \bull\tt\dashrightarrow Diameter=2(4.2)[/tex]
[tex]\\ \bull\tt\dashrightarrow Diameter=8.2m[/tex]
Answer:
Solution given:
radius [r]=4.2m
since
diameter is twice of radius
so
diameter=2*radius=2*4.2=8.4m
option B.8.4m