3. a+b+c+d=340
a+b+c=300
b+c+d=260
b=4c
a+b+c+d=340
300+d=340/-300
d=40
b+c+d=260
b+c+40=260 /-40
b+c=220
4c+c=220
5c=220 /:5
c=44
b=4 x c
b=4x44
b=176
a+b+c=300
a+176+44=300
a+220=300/-220
a=80
4. a+b+c=654
b:a=11,r 10 => b=11a+10
c:a=25,r 15 => c=25a+15
a+b+c=654
a+11a+10+25a+15=654 /- 25 ( =10+15)
37a= 629 /:37
a=17
b=11x17+10
b=187+10
b=197
c=25x 17 +15
c=425+15
c=440
