Find the mean of the following frequency distribution:

C.I. & x & f & \(\displaystyle \mathbf{u}=\frac{\boldsymbol{x}-\mathbf{4 2} \boldsymbol{-}}{\mathbf{5}}\) & fu $\displaystyle 25$-$\displaystyle 30$ & \(\displaystyle 27 \cdot 5\) & $\displaystyle 14$ & -$\displaystyle 3$ & -$\displaystyle 42$ $\displaystyle 30$-$\displaystyle 35$ & $\displaystyle 32.5$ & $\displaystyle 22$ & -$\displaystyle 2$ & -$\displaystyle 44$ $\displaystyle 35$-$\displaystyle 40$ & $\displaystyle 37.5$ & $\displaystyle 16$ & -$\displaystyle 1$ & -$\displaystyle 16$ $\displaystyle 40$-$\displaystyle 45$ & $\displaystyle 42.5$ & $\displaystyle 6$ & $\displaystyle 0$ & $\displaystyle 0$ $\displaystyle 45$-$\displaystyle 50$ & \(\displaystyle 47 \cdot 5\) & $\displaystyle 5$ & $\displaystyle 1$ & $\displaystyle 5$ $\displaystyle 50$-$\displaystyle 55$ & $\displaystyle 52.5$ & $\displaystyle 3$ & $\displaystyle 2$ & $\displaystyle 6$ $\displaystyle 55$-$\displaystyle 60$ & \(\displaystyle 57 \cdot 5\) & $\displaystyle 4$ & $\displaystyle 3$ & $\displaystyle 12$ & & $\displaystyle 70$ & & -$\displaystyle 79$Mean \(\displaystyle =42 \cdot 5-\frac{79}{70} \times 5=36 \cdot 86\)