The distance of a planet from its sun is 19000000 miles. if there are 29400000 seconds in one orbit, find the speed of the planet in its orbit about the sun. (assume a circular orbit)

Orbit circumference

= 2 pi * 1.9*10^7 miles

time for orbit trip = 2.9*10^7 s

speed = 2 pi * 1.9 / 2.9 miles/second

= 4.12 miles/second

You did not say what units

in miles per hour, multiply by 3600 and get

14,820 miles/hour