I cannot solve the second part

Two narrow slits are illuminated by a laser with a wavelength of 550 nm. The interference pattern on a screen located x = 5.00 m away shows that the third-order bright fringe is located y = 8.10 cm away from the central bright fringe. Calculate the distance between the two slits.
1.02×10-2 cm
(B) The screen is now moved 2.1 m further away. What is the new distance between the central and the third-order bright fringe?

Question

I cannot solve the second part

Two narrow slits are illuminated by a laser with a wavelength of 550 nm. The interference pattern on a screen located x = 5.00 m away shows that the third-order bright fringe is located y = 8.10 cm away from the central bright fringe. Calculate the distance between the two slits. 
1.02×10-2 cm 
(B) The screen is now moved 2.1 m further away. What is the new distance between the central and the third-order bright fringe?

anonymous · Answer

just use the ratio of change of the size of the triangle.

5m*1.42=7.1m (new distance)
ratio is 1.42

1.42*8.1cm=11.5cm