Kayla and her children went into a restaurant and she bought 63 dollars worth of hotdogs and tacos. Each hotdog costs 3.50 dollars and each taco costs 4 dollars. She bought 3 more hotdogs than tacos. Write a system of equations that could be used to determine the number of hotdogs and the number of tacos that Kayla bought. Define the variables that you use to write the system.