Hi there,
Although I am new to freelancer.com, I have plenty of experience lecturing and tutoring at high school and college in Spain and in the UK. In addition, I hold two PhD degrees in subjetcs related to your problem.
Given that this would be my first project here, I am commited to make this one perfect. Have already done the calculations in detail in GIF files that are ready to be sent.
In any case, here you have the answers:
a) 10^5
b) 10^5
c) 250 km
Looking forward to hearing from you soon.
Best, Daniel