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I'm not sure what is meant by "scalar" projection, but, calling  V₁ = (3,5)   and V₂  = ( 7, -2), the projection of   V₁ onto V₂ is given by :

proj _V2  V₁  =    [V₁ * V₂] * [ V₂ ]

                        ------------

                         ll  V₂  ll ²

V1 * V2   = [3 *7 + 5 (-2)] =  [21 - 10  ]  =   11

ll V2 ll ²  =  7² + (-2)²  = 49 + 4   = 53

So

proj _V2  V₁  =    [11] * [ V₂ ]       =   < 77/53 , -22/53  >

                        -------

                         [53]

2) V₁ + V₂   =  < 3 + 7 , 5 +  - 2 >   =  < 10, 3  >

3) V₁ - V₂  = < 3 - 7, 5 - (-2) >   =  < -4, 7  >

4) V₂ - V₁  =  < 7 - 3, -2 - 5>   = < 4,  -7  >