# How to calculate the velocity gradient at the wall normal to the wall (Boundary layers)?

This problem is from "Fundamentals of aerodynamics" by John D. Anderson, Jr (Fifth edition, page 101):

Consider a flat plate at zero angle of attack in a hypersonic flow at Mach 10 at standard sea level conditions. At a point 0.5 m downstream from the leading edge, the local shear stress at the wall is 282 N/m^2. The gas temperature at the wall is equal to standard sea level temperature. At this point, calculate the velocity gradient at the wall normal to the wall.

I already know: $\tau_w = \mu\left(\frac{dV}{dy}\right)_{y=0} = 282$
but how to get $\mu$ ??

Also I don’t know what this is for: “The gas temperature at the wall is equal to standard sea level temperature”