PLEASE SOLVE C AND D

7.35 A river traveling at a velocity of 10km/ day has a dissolved-oxygen content of 5mg/L and an ultimate CBOD of 25mg/L at distance x=0km, that is, immediately downstream of a waste discharge. The waste has a CBOD decay coefficient k1 of 0.2 /day. The stream has a reaeration rate coefficient k2 of 0.4 / day and a saturation dissolved-oxygen concentration of 9mg/L. (a) What is the initial dissolved-oxygen deficit? (b) What is the location of the critical point, in time and distance? (c) What is the dissolved-oxygen deficit at the critical point? (d) What is the dissolvedoxygen concentration at the critical point