Linear Programming Problems? Find the corresponding values of the slack variables.

So i'm not sure where this question would fit within the categories given, but it is a linear programming problem and it is as follows:

Consider the linear programming problem

Maximize z=2x+5y

subject to

2x+3y$\displaystyle \leq$10

5x+y$\displaystyle \leq$12

x+5y $\displaystyle \leq$ 15

x$\displaystyle \geq$0, y$\displaystyle \geq$0

Part (a): verify that x=[1] (this is a vector) is a feasible solution. For part (a) i

[2]

had no problems verifying it but I need it for part (b)

Part (b) For the feasible solution in a, find the corresponding values of the slack variables.

I started setting it up in canonical form but there are three constraints but two items in the vector given in (a) so i'm stuck. I had started adding in the slack variables as in: 2x+3y+u=10 etc.. but I don't know how to do this one when there are three constraints and two items in the vector.