we will decompose these forces into x and y components, and apply Newton’s second law

call theta the angle of the bank; then, use geometry principles to show that theta is also the angle between a vertical line and the direction of the normal force

this enables us to write the x and y components of the normal force as:

x component = N sin (theta)
y component = N cos (theta)

the y component must balance the weight, so we have

N cos (theta) = mg (eq 1)

and the x component must produce the centripetal force, so we have

N sin(theta) = mv^2/r (eq 2)

divide equation (2) by equation (1) to get:

sin (theta)/cos(theta) = v^2/rg

or tan(theta) = v^2/rg

for the data here, we have

tan(theta) = (16.7m/s)^2/(400m x 9.8m/s/s)

tan(theta) = 0.07 or theta = 4.05 deg

(note that you should convert km/hr to m/s)