What Is the Magnitude of the Magnetic Field at Point $\frac { 9 \mu _ { 0 } I } { 16 R }$

Multiple Choice

What is the magnitude of the magnetic field at point P if a = R and b = 2R?

A) $\frac { 9 \mu _ { 0 } I } { 16 R }$
B) $\frac { 3 \mu _ { 0 } I } { 16 R }$
C) $\frac { \mu _ { 0 } I } { 4 R }$
D) $\frac { 3 \mu _ { 0 } I } { 4 R }$
E) $\frac { 3 \mu _ { 0 } I } { 8 R }$