a constant current of $\displaystyle 3A$ for $\displaystyle 4$ hours is required to charge an automotive battery. If the terminal voltage is $\displaystyle 10 + t/2\ V$, where $\displaystyle t$ in hours

(a) how much charge is transported as a result of the charging?

(b) how much energy is expended?

(c) the much does the charging cost? Assume electricity costs $\displaystyle 9 cents/kWh$

first was wondering the why the expression $\displaystyle 10 + t/2\ V$ is used

thanks again for help