13. (L+l)×2=105,2cm
L+l=105,2:2=52,6
L=l×3
l×3+l=52,6
4l=52,6
l=52,6:4=13,15cm
L=3×13,15=39,45cm
14.x+y=32,45
z+w=403,009
(x+y+z+w):4=(32,45+403,009):4=435,459:4=108,86475
15. D- 1003,9 = 423,504
D= 423,504 + 1003,9
D = 1427,404
16.52 ,34 - 3 ,15 = 49 ,19
49 ,19 ⇒ 49 ,2
17.5,621 - 3,823 + 15,2199 = 1,798 + 15,2199 = 17,0179⇒17,0