Answer:
The question was dealt with as an incomplete question.
A. The frictional force is in the positive X direction
B. The net force is in the horizontal direction, f is the friction force in each wheel. so the answer is Fnet=4f
C. The weight is distributed equally on each wheel in the Y direction, gives us the formula 4Nwheel-mg=0 with a final answer of N=mg/4
D. torque force at each wheel is tau=rf, linear acceleration is obtained from the sum of the forces 4f=ma, f=tau/r and f=ma/4, (ma/4=tau/r) giving us the final answer of a=4tau/mr (please note that the tau symbol is in the drop down list and looks like a cross between a lowercase r and an upper case T)