Answer:
Error: Sariah treated every term as though it were an x-term. 5 and -4.5 are constants that cannot be combined with the x-terms. They can only be combined with each other.
Correct solution: 31x + 0.5
Strategy: Pay attention to the variables.
Explanation:
In her first step, it appears Sariah added 13x and 5 to get 18x. These terms are not like terms, so cannot be added in this way. An appropriate strategy is to first identify all the terms with the same variables (x in this case), then add their coefficients.
... = x(13 +17 +1) +5 -4.5
Likewise, all the constant terms can be added.
... = 31x +(5 -4.5)
... = 31x + 0.5