If it took them 15 hours to go 735 miles, and you are trying to find the average rate, then divide the miles by the time (in hours), so for this specific problem, it would be 735 divided by 15 hours, and you will find the answer as 49. (MPH)
A sustainable NGO is one that can continue to fulfil its mission over time and in so doing meets the needs of its key stakeholders – particularly its beneficiaries and supporters.