In the figure shown, L1, L2 and L3 intersect at the same point. If the ratio of y to x is 3 and the ratio of z to x is 5, then what is the value of y?
Note: If lines intersect, then the vertical angle are equal in measure. When a ratio of two variables is equal to a constant, we get an equation of these two variables. Use the substitution method to change three variables equation into one variable equation, then we can get the value of y.