I need help with this question, please do it in steps!

3x-y=5

2.30+0.4-0.88+1.33 can u explain the answer to this why the answer is 3.15

David is spreading mulch on a triangular area of his flower bed. the coordinates of the vertices of the area are (1, 3), (9, 3), and (4, 6). what is the area of the triangle if each square has an area of 3 square feet?

What are the solutions of the system? solve by graphing. y = -x^2 - 3x + 2 y = -2x + 2