  We present results from spectral fitting of the very high state of GX~339-4
with NuSTAR and Swift. We use relativistic reflection modelling to measure the
spin of the black hole and inclination of the inner disk, and find a spin of
$a=0.95^{+0.02}_{-0.08}$ and inclination of $30${\deg}$\pm1$ (statistical
errors). These values agree well with previous results from reflection
modelling. With the exceptional sensitivity of NuSTAR at the high-energy side
of the disk spectrum, we are able to constrain multiple physical parameters
simultaneously using continuum fitting. By using the constraints from
reflection as input for the continuum fitting method, we invert the
conventional fitting procedure to estimate the mass and distance of GX~339-4
using just the X-ray spectrum, finding a mass of $9.0^{+1.6}_{-1.2}M_\odot$ and
distance of $8.4\pm0.9$ kpc (statistical errors).
