If the gravitational field in the space is given as (- K r ^ 2 ) ....

Given, $E = - \dfrac{K}{{r}^{2}}$

Gravitational field and gravitational potential is related as $E = - \dfrac{d V}{d r}$

So, $- \dfrac{d V}{d r} = \dfrac{- K}{{r}^{2}}$

Integrating the above relation,

${∫}_{10}^{V} d V = {∫}_{2}^{3}\dfrac{K}{{r}^{2}} d r$

$⇒ V - 10 = K\left[\dfrac{1}{2} - \dfrac{1}{3}\right]$

$⇒ V - 10 = \dfrac{K}{6} ⇒ V = \dfrac{6}{6} + 10 ⇒ V = 11J{kg}^{- 1}$