A 10kg crate is already sliding across a factory floor. A worker pushes straight downward on the top of the crate with a force of 30N while also pushing it horizontally. If the coefficient of kinetic friction between the crate and the floor is 0.35 and g=9.8m/s2, which value is closest to the magnitude of the kinetic friction force acting on the crate?
a) 34N
b) 128N
c) 45N
d) 64N