[tex]\begin{gathered} \tan (A-B)=\frac{\tan A-\tan B}{1+\tan A\tan B} \\ \tan A=\frac{21}{20} \\ \text{tan B=?} \\ \text{cosB}=\frac{28}{53} \\ b=28 \\ h=53 \\ h^2=p^2+b^2 \\ p^2=53^2-28^2 \\ p^2=(53+28)(53-28) \\ p^2=81\times25 \\ p=\sqrt[]{2025} \\ p=45 \\ \tan B=\frac{45}{28} \\ \tan (A-B)=\frac{\frac{21}{20}-\frac{45}{28}}{1+\frac{45}{28}\times\frac{21}{20}} \\ =\frac{1.05-1.607}{1+1.05\times1.607} \\ =-\frac{0.557}{2.687} \\ =-0.207 \end{gathered}[/tex]
