Question 1129307
1.C=400+8t
2.C=800+4t
3.{{{graph(300,300,-10,110,-100,1400,400+8x,800+4x)}}}
4. 400+8t=800+4t, substituting for C
4t=400
t=100 months
5.C=400+8t
-C=-800-4t
0=-400+4t
4t=400
t=100, C=1200
6.Intersection is the breakeven point.
7.  The solutions are the same graphically, with substitution and elimination.
8. If one is going to have the refrigerator for more than 8 1/3 years, the more expensive one would be cheaper. If one were not going to have it for that long, the cheaper one would save money although it would use more electricity.