If by "coincide", in other words this is also known as intersect, it means that the solution to the system is that intersection point. For instance, if the intersection point of the 2 lines is (5,7) on the graph, it means that in both equations, x = 5 and y = 7. If you mean that the 2 equations result in the same line, it means that the 2 equations were really equal, but that one could be basic to be identical with the other. For example, if you have 2x + 2y = 8 and 4x + 4y = 16, they will give you the same line, and you can see that if you divide that second equation by 2 all the way crossways, it merely shows the first equation.
        
             
        
        
        
Answer:
27
Step-by-step explanation:
15x-31 = 9x+11
6x-31 = 11
6x = 42
x = 7
15x -31 + 9x + 11 + s = 180
15(7) -31 + 9(7) + 11  + s = 180
105 - 31 + 63 + 11 + s = 180
153 + s = 180
s = 27
 
        
             
        
        
        
Answer:
Step-by-step explanation:
if the slopes are same then parallel.
if the product of slopes=-1 then perpendicular.
 
        
             
        
        
        
Step-by-step explanation:
Part A, Option 1 is a exponential function while option is a linear equation. 
Part B, Let y=b*a^(x) be the function for option 1. At x=1, y=1100 and at x=2, y=1210. 1100=b*a and 1210=b*a^2. Dividing them both we get, b=1.1 and a=1000. y=1000*(1.1)^(x). For option 2, it's a linear equation with a function y(x)=1000+100x. 
The 20 year difference would be immense. With option 1, Belinda will get $6727.5 whereas with option 2, they will end up with $3000