Suppose that in one week, your company takes in $2,220 in sales at one of its cell phone stores. The price breakdown per phone is as follows:
Cell phone model A4: $35
Smartphone Z20: $50

Suppose that a total of 51 phones were sold.

this is the supposed problem with the method of solving in a graph

Question

Suppose that in one week, your company takes in $2,220 in sales at one of its cell phone stores. The price breakdown per phone is as follows:
Cell phone model A4: $35
Smartphone Z20: $50

Suppose that a total of 51 phones were sold.
  
this is the supposed problem with the method of solving in a graph

anonymous · Answer

Standard form: a+z=51; 35a+50z=2220; 
substitute/eliminate a = -1z+51
substitute/eliminate z = +29
Solution: a = 22; z = 29;