The speed of 4m/s means that the bike goes 4 meters for each second of movement. Multiplying this by 5 seconds we have a total distance travelled of 20m.
Friction force is the force that one object exerts in another when the two rub against each other. Most of the time, friction force opposes the motion of an object.
According to the Pythagorean Theorem for calculating the lengths of a right angle triangle's sides, a^2 + b+2 = c^2, where c is the longest side (and the side opposing the right angle). So in your case it would be 150*150 + 70*70 = 27400. And √ 27400 is your answer.
