Answer:
a
 the displacement of the plane is  
b
 The displacement of plane  from Portland to Akron with layover at Houston is  
         
 
c
   the vector which defines this displacement is  
Step-by-step explanation:
From the question we are the 
    The displacement from Portland, Oregon to Houston, Texas. is  
     The displacement  from Houston, Texas to Akron, Ohio.  is  a
a
a 
    The motion of the plane in question a is in the opposite direction to vector 
So the displacement of the plane is  
b 
The motion of Portland to Houston to Akron is in the direction of both vector  and
 and   so
  so 
 The displacement of plane  from Portland to Akron with layover at Houston is  
         
 
c
 From the question we are told that the plane flies over Portland to get to  Anchorage, Alaska which implies that it is moving in opposite direction to the vector 
    Give that distance from Portland to Houston is  
            and the distance from Portland to  Anchorage is  km
km
Then the vector which defines this displacement is mathematically represented as 
    
     