Suppose the demand function for $x$ thousand $of$ a certain item $isp=150+\frac{70}{lnx},$ where $x>1$ and $pisin$ dollars.

$(a)$ Find the marginal revenue.

$(b)$ Find the revenue from the next thousand items $at$ a demand $of6000(x=6).$

$(a)$ The marginal revenue function $is{R}^{\text{'}}(x)=$

$.$

$(Use$ integers $or$ fractions for any numbers $in$ the expression.$)$