Express x = 2sin(0.5t + 3) + 3cos(0.5t + 1) in the form x = Rsin(0.5t + ø)

All working must be done in radians.

I am stuck trying to solve this question.

I understand that:

asinx + bcosx can be written as Rsin(x + ø)

Where: Tanø = b/a and: R = sqrt(a² + b²)

The values for x (the frequency) in the question however have different numbers added to them. Does anyone know how to get around this? Thanks