You want at least three food items for each of the 35 guests. That means you want at least 3(35) = 105 bratwursts or hamburgers. You can write this equation:
(number of bratwursts) + (number of hamburgers) (is at least) 105
x + y ≥ 105
Bratwursts cost $1.30 each and hamburgers cost $1.20 each. Your budget is $150. So, you want the cost of the food items to be less than or equal to $150. You can write this equation
(cost of bratwursts) + (cost of hamburgers) ≤ 150
(price of one bratwurst)(number of bratwursts) + (price of one hamburger)(number of hamburgers) ≤ 150
1.3x + 1.2y ≤ 150