a man walks foward on a bus. to a stationary obserrver, the bus moves east at a speed of 18 m/s if the man moves 1.5 m/s wast relative to the bus. what is his velocity in the frame of reference of a stationary observer?

You said that the bus is moving east and the man is walking west relative to the bus. So it's clear to me that the man is walking from the front toward the back of the bus.

In the frame of reference of the stationary observer:

(18 m/s east) + (1.5 m/s west) = 16.5 m/s east.