18)A tank with rectangular base and rectangular sides, open at the top is to be constructed so that its depth is 2 m and volume is 8 cubic metres. The building of tank costs Rs70 per sq.metres for the base and Rs45 per square metre for the sides.
Based on the above information, answer the following: [PLS ANSWER ALL 5 QUESTIONS BELOW BECAUSE THEY ARE PART OF A SINGLE QUESTION] (with steps)

(i) If x and y represents the length and breadth of the rectangular tank, then the relation between the variables in terms of volume is
a) y = 4/x
b) x = 4/y
c) 2(xy+2y+2x)=8
d) xy +2y+2x = 8

(ii) The area of the 4 walls of the rectangular tank in terms of x and y is
a)4x+2y
b) 4x+4y
c)2x+4y
d)2x+2y

(iii) The total cost of buiding the tank is
a)Rs ( 40x+40y)
b) Rs (80x+80y)
c) Rs (120x+120y)
d)Rs (180x+180y)

(iv) The manufacturer of the tank is interested in minimizing the expense of the tank during construction. For this to happen the valve of x should be
a) 3 m
b) 5 m
c) 2 m
d) 8 m

(v) The minimum cost of construction of the tank is
a)Rs 2000
b) Rs 3000
c) Rs 1000
d) No minimum cost