Answer:
The girl threw the marshmallow with a speed of 35.4 m/s.
Step-by-step explanation:
Use the formula for the range of projectile motion:

with R the range or distance (92m), theta the elevation angle (67 degrees) and g the gravitational acceleration. The velocity can be determined from this as follows:

The girl threw the marshmallow with a speed of 35.4 m/s, which is approximately 79 mph. No word on the boy's condition after the marshmallow's landing.