A glider moving with a speed of 200 kilometers/hour experiences a cross wind of 30 kilometers/hour. What is the resultant speed of the glider relative to the ground?

You didn't say so, but we must assume that the "200 km/hr" is

the glider's air-speed, that is, speed relative to the air.

If the air itself is moving at 30 km/hr relative to the ground and

across the glider's direction, then the glider's speed relative to

the ground is

√ (200² + 30²)

= √ (40,000 + 900)

= √ (40,900) = 202.24 ... km/hr (rounded)