b. \( 15+28= \)

Did you know that the numbers 15 and 28 are both part of a group called "triangular numbers"? Triangular numbers represent objects arranged in the shape of an equilateral triangle. When you add them together, you get 43, which might not be a triangular number itself, but it's still pretty fascinating to see how numbers connect in this way! In real-world applications, addition like this comes in handy all the time. For instance, if you're planning a party and you have 15 guests from one group and 28 from another, knowing you have 43 attendees helps you prepare seating and food! It's amazing how simple math can assist in organizing events!