A river flows from north to south. The position at time t seconds of a rowing boat crossing the river from west to east is modelled by the parametric equations x = 0.9 t m, y = −3.2 t m where x is the distance travelled east and y is the distance travelled north. Given that the river is 75 m wide, 

a. Find the time taken to get to the other side 

b. Find the distance the boat has been moved off-course due to the current 

c. Show that the motion of the boat is a straight line 

d. Determine the speed of the boat.