Create an equation that models the given context
The total salary of an employee consists of fixed salary and overtime payment proportionate to his working hours.
Let's say the fixed salary of the employee is represented by 'x' while their overtime payment is based on the hourly rate, 'h' multiplied by the number of overtime hours, 'y'. The total salary, 's' of the employee can be modeled by the equation: 

s = x + hy