Which of the Following Algebraic Expressions Is the Ploughback Ratio $\times$

Which of the following algebraic expressions is the ploughback ratio? (b is the fraction of earnings retained in the firm and g is the growth rate.)

A) g = (1 - b) $\times$ ROE
B) g = ROE $\div$ b
C) g = b $\times$ ROE
D) g = (1 + b) $\times$ ROE