5. ab-ac=a(b-c) = 240,
Dar b-c=8, deci ax8=240
a=240:8=30
a=30
6. 3a+6b=54
3(a +2b)=54,
Dar a+2b=54:3=18
a+2b=18
14. 4a+8b=200
4(a+2b)=200
a+2b=200:4=50
14b+7c=140
7(2b+c)=140
2b+c=140:7=20
a+2b-(2b+c)= a+2b-2b-c= a-c=
= 50-20=30
a+2b+(2b+c)= a+2b+2b+c= a+4b+c=
= 50+20 = 70
(a-c)(a+4b+c)=30 x70 =2100
