S=a+b+c+d
a=75%(b+c+d) =75%(S-a)=3(S-a)/4 4a=3S-3a 7a=3S a=3S/7
b=40%(a+c+d) =40%(S-b) =2(S-b)/5 5b=2S-2b 7b=2S b=2S/7
c=2/19(a+b+d) =2/19S-c) = 2(S-c)/19 19b=2S-2b 21b=2S c=2S/21
d=4/17(a+b+c) =4/17(S-d) =4(S-d)/17 17d=4S-4d 21d=4S d=4S/21
(a+c)-(b+d)=5
3S/7+2S/21-2S/7-4S/21=5
9S+2S-6S/7-4S=105
S=105
a=3S/7 =3*105/7=45
b=2S/7 =2*105/7= 30
c=2S/21 =2*105/21=10
d=4S/21 =4*105/21=20