To answer this question we will set and solve a system of equations.
Let M be the number of shares of Mazda that were bought, and H be the number of shares of Honda. Then we can set the following system of equations.

Subtracting M from the first equation we get:

Substituting the above equation in the second one we get:

Applying the distributive property we get:

Adding like terms we get:

Subtracting 2400 from the above equation we get:

Dividing the above equation by 2.4 we get:

Substituting the above equation at H=500-M we get:

Answer: 320 shares in Mazda and 180 shares in Honda.