# Weird answer for "Solving systems of linear equations" in SAT math section

This was the math problem.

*1.5a - 4.5b = 3(a + b)*

*5.5b = 5(b - a) + 2.5a*

*Consider the system of equations above. If (a,b) is the solution to the system, then what is the value of b - a?*

This is the solution Khan Academy gave.

A part of the solution confused me. I understood how they reached

*5.5b = 30b - 12.5b*, but I don't understand how*b = 0*. Shouldn't*b = 12*?
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