Official solution
Required area
\[ = \int\limits_1^4 {\left( {\sqrt {8x} - \sqrt 2 x} \right)dx} \]
\[ = \left. {{{2\sqrt 8 } \over 3}{x^{{3 \over 2}}} - {{{x^2}} \over {\sqrt 2 }}} \right|_1^4\]
\[ = {{16\sqrt 3 } \over 3} - {{16} \over {\sqrt 2 }} - {{2\sqrt 8 } \over 3} + {1 \over {\sqrt 2 }}\]
\[ = {{11\sqrt 2 } \over 6}\] sq. units