Let $y = f ( x )$ be the solution to the differential equation $\frac { d y } { d x } = x - y$ with initial condition $f ( 1 ) = 3$. What is the approximation for $f ( 2 )$ obtained by using Euler's method with two steps of equal length starting at $x = 1$ ?
(A) $- \frac { 5 } { 4 }$
(B) 1
(C) $\frac { 7 } { 4 }$
(D) 2
(E) $\frac { 21 } { 4 }$