(3X-1,80)/2,4 = 3,2
(3X-180:100)/24:10 = 32:10
(3X-9/5)/12/5 = 16/5
(3X-9/5)×5/12 = 16/5
(15X-9)/5×5/12 = 16/5
(15X-9)/12 = 16/5
5×(15X-9) = 16×12
75X-45 = 192
75X = 192+45
75X = 237
X = 3,16
2×(0,5X+1) = - 7,2
2× (5X/10+1) =- 72/10
2×(5X+10)/10 = -72/10
(10X+20)/10 = -72/10
10(10X+20) = -72×10 |:10
10X+20 = -72
10X = -72-20
10X = - 92
X = - 92:10
X = - 9,2