Assuming that $ f(x)$ is a continuous function over the interval $[2,10]$, the following table gives the function values for selected values of $x$. Forming a Left Riemann Sum using the intervals of width $2$ suggested by the table, find the value of $k$ given the approximation of the following integral:

$$\int _{ 2 }^{ 10 }{ f( x ) dx } =90$$

$x$ | 2 | 4 | 6 | 8 | 10 |
---|---|---|---|---|---|

f(x) | 15 | 13 | 10 | k | 8 |