The answer would be 10 hours using the formula y = 34.50n+375 with n being the number of hours and y being the total cost. You can find out the equation by finding out which is a constant variable and which one changes. For example the 375 dollars cost in materials wont change but the 34.50 dollars per hour could vary depending in how many hours. Now you can either graph this equation or plug in different values for n until you get the answer.