Basically you find the the two tangents
for 2x+y=10
m=-2
for 12/x
dy/dx= -12/x2
m= -3
also because tan theta= m
for eq 1
theta= tan-1 (-2)
= -63.4(negative sign is cuz of the direction) =63.4
for eq 2
theta= tan-1 (-3)
=-71.6=71.6
angle between them would be the difference...
Draw graphically if u don't understand
71.6-63.4=8.2 degrees