From the condition, you have these two equations


x + y = 152    (1)   (x = the first stage burning time)
x - y = 28     (2)


Add the two equations. You will get  


2x = 152 + 28 = 180  ====>  x = 90 seconds for the first stage.


Then y = 152 - 90 = 62 seconds for the seconf stage.