I need help with THIS optimization problem (do not include Cj in you answer there is no Cj it says budget of k)

Suppose we are given n potential facility locations and a list of m clients who need to be serviced from these locations. We only have a budget for opening a number of these locations (for example, this number is k). There is a cost dijof serving client i from facility . Formulate an optimization model that select a set of facility locations and assign each client to one facility, while minimizing the total cost of serving the clients