15 )
b1+b2+b3=257
b1=b2+15
b1=b3-1 7
b1+b1+15+b1+17=257
3× b1=257-15-17
3×b1=225
b1= 225:3
b1=75
b2=75+15=90
b3=75+17=92
17)
a+b+c=740
a-y=115
b-y=120
c-y=124
y+115+y+120+y+124=740
3y= 740-115-120-124
3y=381
y= 381÷3
y=127
a =127-115
a=12
b=127-120
b=7
c=127-124
b=3
