`9)`
`12x-15>30-3x`
`<=>12x+3x>30+15`
`<=>15x>45`
`<=>15x*1/15>45*1/15`
`<=>x>3`
`10)`
`7x-3>2x+12`
`<=>7x-2x>12+3`
`<=>5x>15`
`<=>5x*1/5>15*1/5`
`<=>x>3`
`11)`
`14x+13<20-7x`
`<=>14x+7x<20-13`
`<=>21x<7`
`<=>21x*1/21<7*1/21`
`<=>x<1/3`
`12)`
`2x+1≥4-x`
`<=>2x+x≥4-1`
`<=>3x≥3`
`<=>3x*1/3≥3*1/3`
`<=>x≥1`
9: =>15x>45
=>x>3
10: =>5x>15
=>x>3
11: =>21x<7
=>x<1/3
12: =>3x>=3
=>x>=1
9, 12x-15>30-3x
<=>12x-15+3x>30
<=>15x>45
<=>x>3
10, 7x-3>2x+12
<=>7x-3-2x>12
<=>5x-3>12
<=>5x>15
<=>x>3
11, 14x+13<20-7x
<=>14x+13+7x<20
<=>21x+13<20
<=>21x<7
<=>x<\(\dfrac{1}{3}\)
9)12x-15>30-3x
<=>12x+3x>30+15
<=>15x>45
<=>\(15x\cdot\dfrac{1}{15}>45\cdot\dfrac{1}{15}\)
<=>x>3
10)7x-3>2x+12
<=>7x-2x>12+3
<=>5x>15
<=>\(5x\cdot\dfrac{1}{5}>15\cdot\dfrac{1}{5}\)
<=>x>3
11)14x+13<20-7x
<=>14x+7x<20-13
<=>21x<7
<=>\(21x\cdot\dfrac{1}{21}< 7\cdot\dfrac{1}{21}\)
<=>x<\(\dfrac{1}{3}\)
12)2x+1≥4-x
<=>2x+x≥4-1
<=>3x≥3
<=>\(3x\cdot\dfrac{1}{3}\ge3\cdot\dfrac{1}{3}\)
<=>x≥1
