Answer:
26 % of mass is added.
Explanation:
We know that
P V = m R T Â Â Â Â Â Â ------1
P=Pressure
V=Volume
R= Gas constant
T= Temperature
m=Mass
Lets mass added =m'
P'=1.2 P
V'=1.05 V
P' V' = m' R T Â Â Â Â Â
1.26 Â P V = m' R T Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â --------2
Form equation 1 and 2
1.26 = m' /m
m' = 1.26 m
Mass added = m' - m
         Δ m  = 1.26 m - m = 0.26 m
So percentage of mass added  =  Δ m /m
                          =0.26
We can say that 26 % of mass is added.