`A=\sqrt{121}-\sqrt{25}.\sqrt{4}`
`=11-5.2`
`=11-10`
`=1`
`B=\sqrt{18}-2\sqrt{50}+3\sqrt{8}`
`=3\sqrt{2}-10\sqrt{2}+6\sqrt{2}`
`=-\sqrt{2}`
`C=(5-frac{7-\sqrt{7}}{\sqrt{7}-1})(5+frac{\sqrt{7}+7}{\sqrt{7}+1})`
`=(5-frac{\sqrt{7}(\sqrt{7}-1)}{\sqrt{7}-1})(5+frac{\sqrt{7}(1+\sqrt{7})}{\sqrt{7}+1})`
`=(5-\sqrt{7})(5+\sqrt{7})`
`=25-7`
`=18`