Answer:
Nirmala can use the lamp for 31.66 hours before it runs out of oil.
Step-by-step explanation:
From the graph,
Take any two points, let say
(15, 25)
(25, 10)




The equation of line in slope-intercept form

Putting
and any point, let say (25, 10), to find the y-intercept 'b'







So the equation of line will be:


In order to find how long Nirmala can use the lamp before it runs out of oil, we need to find x-intercept which can be obtained by putting y = 0, and solve for x, as duration lies on x-axis.
so

Putting y = 0










Therefore, Nirmala can use the lamp for 31.66 hours before it runs out of oil.