A = lw
l =

w = 50 mm
a = 250 sq. mm
l =

= 5 mm
Hence, the length is 5 mm.
The options seem a bit mis-formatted but here is the way p is computed:
the decrease is 2000-1600
and it is relative to: 2000 (2003 attendance)
so 
and so that aligns with your Option A. Options B, C, D look incorrect for sure.
Answer:
8
Step-by-step explanation:
replace x with 4 and y with 2 in the equation
3x - 7y + 10
3(4) - 7(2) + 10
multiply
12 - 14 +10
add
-2 + 10 = 8