28 x 12 = 336
336 - 16 = 320
320 divided by 4 = 80
80
Lights
X and y are proportional hence when y is multiplied by a number, x is multiplied by the same number.
18=6*3 hence when y=18,x=9*3=27
x=27
1+3+5+7+...+999 =
= 1+2+3+4+...+500
+1+2+3+...+499
= 2·(1+2+3+...+499) + 500
= 2·(499·500)/2 + 500
= 499·500 + 500
= 500·(499 + 1)
= 500·500
= 250.000
