Given is the damage index equation, 
 
 
where y represents damage index, and x represents ambient temperature.
It is similar to slope-intercept form of linear equation given by y = mx + b.
Where m is said to be the slope of line and b is the y-intercept of the line. When x = 0, y = b.
Similarly, if plug x = 0 in the damage index equation, 
 
 
So, If ambient temperature, x = 0. Then damage index, y = 14. 
Hence, option D is correct i.e. " If the ambient temperature is 0 then the damage index would be 14".