In MySQL

I have doubts how is the code written for the following instruction:

Compute the amount to be billed to each project as Amount. The amount for each project is computed as the sum of the amount billed to the project by all employees working on the project. The amount billed by an employee to a project is obtained as the product the hours (HRS) that the employee devotes to the project and the billing rate (E_RATE) for the employee (show only the output of the query).

WORK table PROJECT table EMP(employee) table