Orbits are elliptical, and so the speed and height of the orbit changes continuously. Therefore, we will use the length of the semi-major axis according to Kepler's laws. As a special case, if the orbit is circular, then the speed and height are constant, and the semi-major axis is the radius.
if T is the period, then
( T / 2pi )^2 = a^3 / (GM),
where a is the length of the semi-major axis, G is the gravitational constant, and M is the mass of earth.
for a circular orbit of 150 minutes,
(150x60 / 2pi)^2 = a^3 / ( 6.674e-11 x 5.97e24 )
a^3 = (((150 × 60) / (2 × pi))^2) × 6.67400e-11 × 5.97e24
= 8.17496337e20
a = e^(ln(8.17496337e20) / 3) = 9 350 365.88 m
in other words, the radius is about 9350 km.
the satellite travels 2 pi of these in 150 minutes;
speed = (9 350 365.88 x 2 x pi) / (150 x 60) = 6 527.78683
so 6527.8 m/s