The very peak of the curve. $$v_p = \sqrt\frac2RTM$$ Use this to find the x-coordinate of the highest point on your graph.

The distribution is given by the equation (f(v) = 4\pi \left(\fracm2\pi kT\right)^3/2 v^2 e^-\fracmv^22kT), where (f(v)) is the probability density function, (m) is the mass of the gas molecules, (k) is the Boltzmann constant, (T) is the temperature in Kelvin, and (v) is the speed of the gas molecules.