Answer:
[tex]120 = \frac{b}{4} \sqrt{1156 - {b}^{2} } [/tex]
[tex]b \sqrt{1156 - {b}^{2} } = 480[/tex]
[tex] {b}^{2} (1156 - {b}^{2} ) = 230400[/tex]
[tex]1156 {b}^{2} - {b}^{4} = 230400[/tex]
[tex] {b}^{4} - 1156 {b}^{2} + 230400 = 0[/tex]
[tex]( {b}^{2} - 256)( {b}^{2} - 900) = 0[/tex]
b = ±16, ±30
