A rectangular trough is 8 feet long, 2 feet across the top and 4 feet deep. If water flows in at a rate of 2 ft3 /min, how fast is the surface rising when the water is 1 ft deep?

a. 1/4 ft/min

b. 1/2 ft/min

c. 1/8 ft/min

d. 1/6 ft/min

the answer for this is letter c 1/8 however i dont know the solution. Please give me solution ffor this through handwritten for better understanding. Thank you