two friends meet at an intersection when they part one walks

two friends meet at an intersection when they part, one walks west at 3 miles per hour while the other walks north at 4 miles per hour. After one minute at what rate is the distance between them (as the crow flies) increasing?

Please explain/ show work for rating. Someone told me 5 mph or 5t but I don\'t understand how the got that. Please show me.