How to solve this question of calculus?

Fred, Noa and Austin meet every day to go tor a walk together. Today, they decide to follow a spiral curve with polar equation 7' = 20. a) After discussing how much of the spiral they should walk, they decide to start at the point corresponding to 9 = 0 and to end at the point corresponding to 0 = 5 1r . Among the plots below, select the one that represents the path walked by Fred, Noa and Austin. \fb) Fred, Noa and Austin take pride in their daily walks and they want to keep track of the lengths they walk. To calculate the length of the curve in part a), they need to evaluate the integral 1=2/V02 + 120, with a = 57 . Using the substitution 0 = sinh(u) , they first obtain de = p(u) du with $(u) = and therefore CB I= g(2) du with g (u ) = and B = An antiderivative of g (u) is G(u) = u + sinh(2u) 2 , from which they conclude that the length I of the curve is sinh -(57) + L, with L =