If the amount of heat given to a system is $35 \ J$ and the amount of work done by the system is $-15 \ J$,then the change in the internal energy of the system is .... $J$.

Given below are two statements. One is labelled as Assertion $A$ and the other is labelled as Reason $R$.
Assertion $A$ : If $dQ$ and $dW$ represent the heat supplied to the system and the work done on the system respectively,then according to the first law of thermodynamics $dQ = dU - dW$.
Reason $R$ : The first law of thermodynamics is based on the law of conservation of energy.
In the light of the above statements,choose the correct answer from the options given below:

When $2 \ kg$ of water is boiled at atmospheric pressure,it converts into steam. The volume increases from $2 \times 10^{-3} \ m^3$ to $3.34 \ m^3$. The work done by the system is ....... $kJ$.

$A$ gas is compressed at a constant pressure of $50 \,N/m^2$ from a volume of $10 \,m^3$ to a volume of $4 \,m^3$. Energy of $100 \,J$ is then added to the gas by heating. Its internal energy is

$1 \,g$ of water at $100^{\circ} C$ is completely converted into steam at $100^{\circ} C$. $1 \,g$ of steam occupies a volume of $1650 \,cc$. (Neglect the volume of $1 \,g$ of water at $100^{\circ} C$). At the pressure of $10^5 \,N/m^2$, the latent heat of steam is $540 \,cal/g$ $(1 \,calorie = 4.2 \,joule)$. The increase in the internal energy (in joule) is:

$540$ calories of heat convert $1$ cubic centimeter of water at $100^{\circ}C$ into $1671$ cubic centimeter of steam at $100^{\circ}C$ at a pressure of one atmosphere. Then the work done against the atmospheric pressure is nearly ...... $cal$.