You can use the law sines, which states that in a triangle the ratio between one side length and the sine of the opposite angle is constant.
So, we have
[tex]\dfrac{PR}{\sin(Q)}=\dfrac{QR}{\sin(P)}=\dfrac{PQ}{\sin(R)}[/tex]
In particular, we can use
[tex]\dfrac{PR}{\sin(Q)}=\dfrac{QR}{\sin(P)}[/tex]
to write
[tex]\dfrac{68}{\sin(73)}=\dfrac{47.6}{\sin(P)} \iff \sin(P) = \dfrac{47.6\sin(73)}{68}\approx 0.66[/tex]
Which means
[tex]P\approx \arcsin(0.66)\approx 42[/tex]
