1.
12 - 10x = 25 - 30x
<=> 12 - 25 = -30x + 10x
<=> - 20x = -13
<=> x = 13/20
2.
3(2x+3) - 2(4x - 5) = 10x+21
<=> 6x + 9 - (8x - 10) = 10x + 21
<=> 6x + 9 - 8x + 10 = 10x + 21
<=> -2x + 19 = 10x + 21
<=> -12x = 2
<=> x = -1/6
1: =>-10x+30x=25-12
=>20x=13
=>x=13/20
2: =>6x+9-8x+10=10x+21
=>10x+21=-2x+19
=>12x=-2
=>x=-1/6