Aerodynamic center is a point on the airfoil for which the aerodynamically generated moment is independent of the angle of attack or the coefficient of lift. Aerodynamic center is at $\frac{1}{4}$ chord from the leading edge for most of the low speed airfoils. For supersonic airfoils aerodynamic center lies nearer at $\frac{1}{2}$ chord length. Location of the aerodynamic center as a fraction of the chord length is given as $$x_{ac}=-\frac{m_{0}}{a_{0}}+0.25$$ $m_{0}$ = Slope of the moment coefficient curve, $$m_{0}=\frac{-0.040-\left ( -0.050 \right )}{4^{\circ}-\left ( -6^{\circ} \right )}=0.001\textrm{ per degree}$$ $a_{0}$ = Slope of the lift coefficient curve, $$a_{0} = \frac{0.70-\left ( -0.35 \right )}{4^{\circ}-\left ( 6^{\circ} \right )}  = 0.105 \textrm{ per degree}$$ Therefore, aerodynamic center lies at, $$x_{ac} = -\frac{m_{0}}{a_{0}} + 0.25$$ $$\Rightarrow x_{ac} = -\frac{0.001}{0.105} + 0.25 = 0.240 \textrm{ chord length}$$