The second question is "not found". For the first, assuming positive direction is right as per the initial driving force, then tension and resistance both act to the left and hence they're negative as would be the acceleration (deceleration). Note Ive not worked through the calcs to find the direction of the tension T, Im just assuming its the same direction as friction as you seem to imply.
If you assumed positive is left, then ma=T+resistance is indeed correct. However, the positive acceleration would be acting left and the initial velocity and resultant displacement would be negative as they are to the right.