The last paragraph is the correct statement. Please don't make me type it all out.
Answer:
The spring constant of this spring is 200 N/m.
Explanation:
Given:
Original unstretched length of the spring (x₀) = 10 cm =0.10 m [1 cm =0.01 m]
Stretched length of the spring (x₁) = 18 cm = 0.18 cm
Force acting on the spring (F) = 16 N
Spring constant of the spring (k) = ?
First let us find the change in length of the spring or the elongation caused in the spring due to the applied force.
So, Change in length = Final length - Initial length

Now, restoring force acting on the spring is directly related to its elongation or compression as:

Rewriting in terms of 'k', we get:

Now, plug in the given values and solve for 'k'. This gives,

Therefore, the spring constant of this spring is 200 N/m.
Answer:
9.45 kWh
Explanation:
Energy = Power × time
E = 900 W × (1.5 h/day × 7 day)
E = 9450 Wh
E = 9.45 kWh
The collapsed answer of Penchalreddy Badepalli is correct. The composition of two reflections via two mirror making an angle \alpha is equivalent to a single rotation by an angle 2\alpha, hence 2 * 60 deg = 120 deg. And turns is independent of the absolute orientation of the two mirrors in space and/or the direction of incidence of the incoming ray.
One could use elementary geometry to prove this (if you presume the direction of incidence is irrelevant imagine hitting the first mirror at 90 deg, then going retro right back along the normal to the first mirror, and follow the directions).