Parallel to the handle, what is the force of friction acting on the suitcase?

 Lets call F the friction force which will act horizontally backwards. 

As you are travelling at a constant velosity horizontally there is no overall resultant force in this direction. 

ie. the force you pull with will be equal to the friction force resisting you. (you will initially have to have pulled with a greater force than the friction to get the suitcase moving) 

the value of your force pulling is 60 cos26.9 (horizontally) - you should have learnt about resolving forces. 

this must be equal to F 

so 

F=60cos26.9 
F=53.5N

hope this helps you
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