Determine which of the following relations are functions and create equations.
a) The relation between earnings and sales if Olwen earns $400 per week plus 5% commission on sales
b) The relation between distance and time if Brian walks at 5km/h

I said they are both functions and created the first equation e=.05s+400 where e=weekly earnings and s=weekly sales. I don't know the second equation, though. Thanks for the help.