[tex]x^2-21.75x=-15.75 \\
x^2-21.75x+15.75=0[/tex]
Use the quadratic formula:
[tex]x^2-21.75x+15.75=0 \\ \\
a=1 \\ b=-21.75 \\ c=15.75 \\ b^2-4ac=(-21.75)^2-4 \times 1 \times 15.75=473.0625-63=410.0625 \\ \\
x=\frac{-b \pm \sqrt{b^2-4ac}}{2a}=\frac{-(-21.75) \pm \sqrt{410.0625}}{2 \times 1}=\frac{21.75 \pm 20.25}{2} \\
x=\frac{21.75-20.25}{2} \ \lor \ x=\frac{21.75+20.25}{2} \\
x=\frac{1.5}{2} \ \lor \ x=\frac{42}{2} \\
x=\frac{15}{20} \ \lor \ x=21 \\
x=\frac{3}{4} \ \lor \ x=21 \\
\boxed{x=\frac{3}{4} \hbox{ or } x=21}[/tex]
