Area to be plastered= [2(l + b) x h] + (l x b)

= [2(25 + 12) x 6] + (25 x 12)

= (444 + 300)

= 744 sq.m

Cost of plastering = Rs.744 x (75/100)

Let the inner and outer radii be r and R metres.

Then   2 ?R = 352 7 = > R = 352 7 * 7 22 * 1 2 = 8 m 

  2 ?R = 528 7 = > R = 528 7 * 7 22 * 1 2 = 12 m

=> Width of the ring = (R - r) = (12 - 8) m = 4 m.

let original radius = r and  new radius = (50/100) r = r/2

original area =  ?r 2 and new area =  ? r / 2 2

decrease in area =  3 ?r 2 / 4* 1 ?r 2 *100 = 75%

A=lb

We know that,

Perimeter of rectangle = 2(L+W) = 2(5 + 2) = 2 (7) = 14 fts.

P=4s

P
= 2l + 2w