\(\Rightarrow \Delta I _{\varepsilon}=\Delta I _{ C }+\Delta I _{ B }\)
\(4 mA =3.5 mA +\Delta I _{ B }\)
\(\Rightarrow \Delta I _{ B }=0.5 mA\)
\(\Rightarrow \beta=\frac{\Delta I _{ C }}{\Delta I _{ B }}\)
\(\beta=\frac{3.5}{0.5}\)
\(\Rightarrow \beta=7\)