To solve your problem, we can apply Newton's second law of motion.
Fⁿ = ma
Fnet = net force acting on the skier
m = mass of the skier = 53 kg
a = acceleration up the slope
Since velocity is constant then acceleration is zero, hence the above equation becomes
Fnet = 0
Fnet = F - Wx - f
where
F = force exerted by the tow bar
Wx = component of skier's weight parallel to the incline = 53(9.8)(sin 20)
f = frictional force = 0.160(53)(9.8)(cos 20)
Substituting appropriate values,
F - 53(9.8)(sin 20) - 0.160(53)(9.8)(cos 20) = 0
and solving for F,
F = 99.55 N
Hope this helps and have a nice day!
