Correct Answer - B
`tan beta = (u sin alpha - g t)/(u cos theta)`
`(sin beta)/(cos beta) = (u sin alpha - g t)/(u cos alpha)`
`u cos alpha sin beta = u sin alpha cos beta beta - g t cos beta`
`g t cos beta = u sin (alpha - beta)`
`u = (g t cos beta)/(sin (alpha - beta))`