The modulus of the complex number $${{3 + 4\,i} \over {1 - 2\,i}}$$ is

Ion concentrations obtained for a groundwater sample (having pH=8.1) are given below.

Ion	$$Ca^{2+}$$	$$Mg^{2+}$$	$$Na^+$$	$$HCO_3^-$$	$$SO_4^{2-}$$	$$Cl^{-}$$
Ionconcentration(mg/L)	100	6	15	250	45	39
Atomic Weight	Ca=40	Mg=24	Na=23	H=1,C=12,O=16	S=32,O=16	Cl=35.5

Total hardness (mg/L as $$CaCO_3$$) present in the above water sample is

Ion concentrations obtained for a groundwater sample (having pH=8.1) are given below.

Ion	$$Ca^{2+}$$	$$Mg^{2+}$$	$$Na^+$$	$$HCO_3^-$$	$$SO_4^{2-}$$	$$Cl^{-}$$
Ionconcentration(mg/L)	100	6	15	250	45	39
Atomic Weight	Ca=40	Mg=24	Na=23	H=1,C=12,O=16	S=32,O=16	Cl=35.5

Carbonate hardness (mg/L as $$CaCO_3$$) present in the above water sample is

The moisture holding capacity of the soil in a 100 hectare farm is 18cm/m. the field is to be irrigated when 50 percent of the available moisture in the root zone is depleted. The irrigation water is to be supplied by a pump working for 10hours a day, and water application efficiency is 75%. Details of crops planned for cultivation are as follows:

Crop	Root zone depth (m)	Peak rate of moisture use(mm/day)
X	1.0	5.0
Y	0.8	4.0

The capacity of irrigation system required to irrigate crop X in 36 hectares is