Pretend that <em>x=1. </em>The first equation is 1=-1+1-0+1 and when you solve that you get 1=1, which is true. To do it step by step: -1+1=0. 0-0=-. 0+1=1.
When you do the same thing to the second equation (<em>x-1</em>), then the equation would be 1=0+(1-0). When you solve the equation, you end up with 1=1, which is also true. Step by step: 1-0=1. 0+1=1.
When adding negative with positive it will always be negative so for this question, subtract -28 with 15 which would be -48. So -48 would be the temperature in the evening.
