#15
[tex]\\ \bull\tt\dashrightarrow x+9>15[/tex]
[tex]\\ \bull\tt\dashrightarrow x>15-9[/tex]
[tex]\\ \bull\tt\dashrightarrow x>6[/tex]
#17
[tex]\\ \bull\tt\dashrightarrow 5x+15\leqslant -10[/tex]
[tex]\\ \bull\tt\dashrightarrow 5x\leqslant -10-15=-25[/tex]
[tex]\\ \bull\tt\dashrightarrow x\leqslant \cfrac{-25}{5}[/tex]
[tex]\\ \bull\tt\dashrightarrow x\leqslant -5[/tex]
#19
[tex]\\ \bull\tt\dashrightarrow 6x\geqslant -0.3[/tex]
[tex]\\ \bull\tt\dashrightarrow x\geqslant \dfrac{-0.3}{6}[/tex]
[tex]\\ \bull\tt\dashrightarrow x\geqslant 0.05[/tex]
#21
[tex]\\ \bull\tt\dashrightarrow \dfrac{1}{4}x>\dfrac{1}{2}[/tex]
[tex]\\ \bull\tt\dashrightarrow x>\dfrac{1}{2}\times 4[/tex]
[tex]\\ \bull\tt\dashrightarrow x>2[/tex]
#23
[tex]\\ \bull\tt\dashrightarrow 2.1x\geqslant 6.3[/tex]
[tex]\\ \bull\tt\dashrightarrow x\geqslant \dfrac{6.3}{2.1}[/tex]
[tex]\\ \bull\tt\dashrightarrow x\geqslant 3[/tex]
