6400+1250=satellite orbit radius=7650
C=2pi*r
(Circumference formula)
7650*2=15300
15300pi=48,066.368
48066.368 is the circumference. It goes around the circumference once every 90 minutes, meaning every 90 minutes it travels 48066.368 km.
48066.368/90min=534.0707511102649
MINUTES:
It's speed is 534.0708 km/min
SECONDS:
It's speed is 8.9012 km/sec