4x-(1/5)x=1.9
4x-0.2x=1.9
3.8x=1.9
x=1.9÷3.8
x=0.5
2.4×5-3x=8
12-3x=8
3x=12-8
3x=4
x=4/3
(6/7)x-4.2×5=21
(6/7)x-21=21
(6/7)x=21+21
(6/7)x=42
x=42÷6/7
x=42×7/6
x=49