Step-by-step explanation:

Hope it will help :)
The equivalence

means that n-5 is a multiple of 12.
that is
n-5=12k, for some integer k
and so
n=12k+5
for k=-1, n=-12+5=-7
for k= 0, n=0+5=5 (the first positive integer n, is for k=0)
we solve 5000=12k+5 to find the last k
12k=5000-5=4995
k=4995/12=416.25
so check k = 415, 416, 417 to be sure we have the right k:
n=12k+5=12*415+5=4985
n=12k+5=12*416+5=4997
n=12k+5=12*417+5=5009
The last k which produces n<5000 is 416
For all k∈{0, 1, 2, 3, ....416}, n is a positive integer from 1 to 5000,
thus there are 417 integers n satisfying the congruence.
Answer: 417
Let lowest possible score be x (66+ 80+ 88+ 82 +72+ x)/6=80 on solving we get ans as 92
(2x - 3y) (4x - y) = 8x² - 2xy - 12xy + 3y²
(2x - 3y) (4x - y) = 8x² -14xy + 3y²
---------------------------------
Answer:8x² -14xy + 3y²
---------------------------------