Answer:
100 kg
Step-by-step explanation:
Two strings are used to hang the painting means the total weight of the painting is split into 2 the two string.
Each string has tension 490 N this means the total weight of the painting is

The tension of both the strings combimed will be the weight of the painting
Weight is given by

where,
m = Mass of the object
g = Acceleration due to gravity =

Here
w = 980 N

So, mass of the painting is 100 kg.