Which angles $\displaystyle \alpha$ will satisfy the equation $\displaystyle \5\sin^2\alpha\ + \25sin\alpha\ - 2.4375 = 0$ ?

I tried the following to no avail.

$\displaystyle \5sin\alpha\(sin\alpha + 1)\ - 2.4375 = 0$

Don't know where to go from here. Maybe use the quadratic formula? Been a while since I've done these.

Thanks