Explanation

(a) Heat is lost by steam in two stages (i) for change of state from steam at $100℃$ to water at $100℃$ is $m \times 540$ (ii) to change water at $100℃$ to water at $80℃$ is $m \times 1 \times (100 - 80),$ where $m$ is the mass of steam condensed
Total heat lost by is $m \times 540 + m \times 20 = 560\ m(cals).$ Heat gained by calorimeter and its contents is $= (1.1 + 0.02) \times (80 - 15) = 1.12 \times 65\ cals$
Using Principle of calorimetery, Heat gained = heat lost
$\therefore 560\ m = 1.12 \times 65,\ m = 0.130\ g$