(1)
2x-0.8×2.6=3.08-2x
4x-2.08-3.08=0
4x-5.08=0
x=1.27
(2)
2.4×0.2x=0.5x-2.4
4.8x-0.5x=2.4
4.3x=2.4
x=24/43
(3)
5(0.2x-2.5)=2.1x
x-12.5=2.1x
-1.1x=12.5
x=-11.36