Please show me the solution , i don't know how to do it

A company plans to place advertisements in two different magazines, A and B. A total budget of $250,000 has been established for these advertisements over the coming year, and the company does not wish to spend less than $100,000 of the budgeted amount. Magazine A gives 1,500,000 effective exposures with each use, and costs $7,500. Magazine B gives 900,000 effective exposures with each use, and costs $5,000; Magazine A is a weekly publication, while magazine B is published once every two weeks. The company does not wish to use magazine A more than 18 times during the year. State this problem as a linear-programming problem, and solve it to nd the optimal number of advertisements to be placed in magazines A and B in the coming year