n a figure, ABCD is a parallelogram in which ∠DAB

In a figure, ABCD is a parallelogram in which ∠DAB = 75^o and ∠DBC = 60^o then ∠BDC is equal to:
.
(a) 75^o
(b) 60^o
(c) 45^o
(d) 55^o