1 atm of pressure corresponds to 760 mmHg. Therefore, we can set a simple proportion to find how many atmospheres of pressure correspond to 633 mmHg, in the following way:

And if we solve this proportion, we find the pressure in atmospheres:
There are several information's already given in the question. Based on those information's the answer can be easily deduced.
Distance traveled by the bicycle rider = 50 km
Time taken to travel the distance = 2.5 hours
So
In 2.5 hours the bicycle rider travels = 50 km
Then
In 1 hour the bicycle rider travels = 50/2.5
= 20 km
Then the average speed of the cyclist is 20 km per hour.
The answer is 3. Photosynthesis removes carbon dioxide while respiration puts back carbon dioxide
2nd and third laws of energy