Volume ratio of decimolar $\mathrm { NH } _ { 4 } \mathrm { OH }$ and decimolar HCl to give a solution of $\mathbf { p H } = \mathbf { 9 . 2 5 }$ at $\mathbf { 2 5 } { } ^ { \circ } \mathbf { C } $ is $\mathbf { x } \boldsymbol { : } \mathbf { 1 }$. Find $\mathbf { x } \boldsymbol { . } \boldsymbol { \rightarrow }$ (2) $\mathbf { p K } _ { \mathbf { b } }$ of $\mathbf { N H } _ { \mathbf { 4 } } \mathbf { O H } = \mathbf { 4 . 7 5 }$