................................................

4b)a+b+c=74 a+b=2*21 b+c=2*28      + ______________ a+b+c+b=98 74+b=98 b=98-74 b=24 a=42-24 a=18 c=56-24 c=32 5b)a+b=28*2 c+d+e+f=2*58 S=56+116 S= 172 5c)x+y+z=3*45 x+y+z+49=ma*4 135+49=m*4 ma=184/4 ma=46