The functions $\mathrm { f } ( \mathrm { x } ) = \mathrm { x } + \mathrm { xi }$ and $\mathrm { g } ( \mathrm { x } ) = 2 \mathrm { x } - \mathrm { xi }$ are defined from the set of real numbers to the set of complex numbers and satisfy
$$f ( a ) + g ( b ) = 4 + 2 i$$
Accordingly, what is the sum $\mathbf { a } + \mathbf { b }$?
A) $\frac { 7 } { 2 }$
B) $\frac { 9 } { 2 }$
C) $\frac { 10 } { 3 }$
D) $\frac { 13 } { 3 }$
E) $\frac { 15 } { 4 }$