What Is the Equivalent Resistance Between Points a and B $\Omega$

Multiple Choice

What is the equivalent resistance between points a and b when R = 30 $\Omega$ ?

A) 27 $\Omega$
B) 21 $\Omega$
C) 24 $\Omega$
D) 18 $\Omega$
E) 7.5 $\Omega$