Tail-Feather Length in Birds Is Sometimes a Sexually Dimorphic Trait

Tail-feather length in birds is sometimes a sexually dimorphic trait. That is, the trait differs substantially for males and for females. Researchers studied the relationship between tail-feather length (measuring the R1 central tail feather) and weight in a sample of 20 male and 21 female long-tailed finches raised in an aviary.
What is the approximate value of the slope for the male regression line (blue squares) ?

A) 3 g/mm
B) 3 mm/g
C) 0.35 mm/g
D) 0.35 g/mm