We must first solve for the 1st lens.
1/p + 1/q = 1/f
1/15 + 1/q = 1/10
1/q = 1/10 - 1/15 = 5/150
q = 150/5 = 30 cm.
The image formed by the 1st lens is 30 cm downstream (to right) from the
Therefore it is 25 cm downstream from the 2nd lens.
The image formed by the first lens becomes the object for the second lens.
Is the object distance for the 2nd lens positive or negative?