During the discharge of a lead storage battery, the density of sulphuric acid fell from 1.294 to 1.139 `g.ml^(-1)`.`H_(2)SO_(4)` of density 1.294 `gml

During the discharge of a lead storage battery, the density of sulphuric acid fell from 1.294 to 1.139 `g.ml^(-1)`.`H_(2)SO_(4)` of density 1.294 `gml^(-1)` is `39%` and that of density 1.139 `g.ml^(-1) is `20%` by weight. The battery holds 3.5 L of acid and the volume practically remains constant during discharge. Calcualte the number of ampere hours for which the battery must have been used. The discharging and charging reactions are:
`Pb + SO_(4)^(2-) rightarrow PbSO_(4) + 2e^(-)` (Anodic reaction)
`PbO-92) + 4H^(+) + SO_(4)^(2-) + 2e^(-) rightarrow PbSo_94) + 2H_(2)O` (Cathode reaction)