Find the Constant K Such That the Function $f ( x ) = k x$

Multiple Choice

Find the constant k such that the function $f ( x ) = k x$ is a probability density function over the interval $[ 3,8 ]$ .

A) 5
B) $\frac { 2 } { 55 }$
C) $\frac { 2 } { 5 }$
D) $\frac { 55 } { 2 }$
E) $\frac { 5 } { 2 }$