How many combinations with repetition are allowed if n equals 4 and R equals 3​

Through non-collinear points there is exactly one plane.

Acar started driving from city a to city b, distance between which is 620 miles, at a rate of 60 mph. two hours later a truck left city b and started moving towards city a at a rate of 40 mph. how many hours after the truck's departure will the two meet?

Polygon abcd is a parallelogram, and m? abc = 127°. the length of is 10 units, and the length of is 5 units. the perimeter of the parallelogram is units, and m? bcd is °