6x-4x=4.2
2x=4.2
x=2.1
6*2.1=12.6
4*2.1=8.4
(12.6+8.4):2=21:2=10.5
а /b=6/4 => a=6b/4
a-b=4.2
6b/4-b=4.2
6b-4b=16.8
b=8.4
a=8.4+4.2=12.6
cр линия=(а+b)1/2*=(12.6+8.4)*1/2*=21*1/2=10.5
