Genetic Algorithm for maximization

this may be a shot in the dark, but I am trying to teach myself more machine learning concepts. I have found a textbook and am trying to work through the exercises in it. Could anyone help me with this example?

Example:

Use genetic algorithm to solve the following optimization problem, including the initialize population, fitness function and each iteration until you find the optimal solution.

max f(x1, x1) = 2x(1)^2 + x(2)^2 + 3x(3)^2

s.t.     x1 ∈{0,1,2,3,4,5,6}
x2 ∈{0,1,2,3,4,5,6}
x3 ∈{0,1,2,3,4,5,6}


Any information that anyone could give me or even resources that work through examples like this would be greatly appreciated. Thanks.