The missing length n on the projection is given as 40. Option d
How to get the missing length
To get the value of n
we have to relate the two triangles with each other such that similar sides of the triangle would divide each other
Hence we have
15 / 30 = 20 / n
from here we have to cross multiply
n * 15 = 20 * 30
15n = 600
n = 600 / 15
n = 40
Hnece the missing length n on the projection is given as 40