I'd guess at valve B. more information about the interesting question would help.
Answer:
Answer is in the following attachment.
Explanation:
We make a graphic of this problem to define the angle.
The angle we can calculate through triangle relation, that is,

With this function we should only calculate the derivate in function of c

That is the rate of change of
.
b) At this point we need only make a substitution of 0 for c in the equation previously found.

Hence we have finally the rate of change when c=0.
Explanation:
There are three forces on the bicycle:
Reaction force Rp pushing up at P,
Reaction force Rq pushing up at Q,
Weight force mg pulling down at O.
There are four equations you can write: sum of the forces in the y direction, sum of the moments at P, sum of the moments at Q, and sum of the moments at O.
Sum of the forces in the y direction:
Rp + Rq − (15)(9.8) = 0
Rp + Rq − 147 = 0
Sum of the moments at P:
(15)(9.8)(0.30) − Rq(1) = 0
44.1 − Rq = 0
Sum of the moments at Q:
Rp(1) − (15)(9.8)(0.70) = 0
Rp − 102.9 = 0
Sum of the moments at O:
Rp(0.30) − Rq(0.70) = 0
0.3 Rp − 0.7 Rq = 0
Any combination of these equations will work.
Given that,
Mass of each washer = 4.9 g
We need to calculate the mass of two washers in kg
Using conversion of unit
Mass of each washer 
So, Mass of two washers is

Put the value of m


If 4 washer are attached to the spring
We need to calculate the applied force on the car
Using formula of force

Put the value into the formula


Hence, (i), The mass of two washers is 0.0098 kg.
(ii). The applied force on the car is 0.192 N.