How many of the following partial differential equations are linear or quasi-linear?
a) yy -15
b) u_{xxx} - 5u_{yyy} = u_{}x^{11} + e^{9x}u_{y}
c)u_{xx} -12u^{14}_{xy} -8u_{yy} =u_{x} +sin(x)u_{y}
d) u_{xx} +3u_{xy} +u_{yy} -3u_{x} +16u_{y} +cos(14u)=0
e) cos u_{xx} - 13u_{xy} - 9u_{yy} = u_{x} + sin(x)u_{}y
f)u_{}t = 12u_{xx}
g)u_{xx} -12u_{xy} -12u_{yy} =u^{8}_{x} +cos(x)u_{y}
h)u_{xx} +2u_{xy} +u_{yy}-4u_{y} +e^{u}=0
i)u_{xx} -16u_{xy} -u^{6}_{yy}=u_{x}+u^{3}_{y}