Part A : His solution is incorrect because whenever you have a number "connected to" the variable, you have to divide. & what you do to one side, you have to do to the other. So, for step 2, instead of subtracting 5, you divide by 5. By doing this, you will then have 'x' by itself on the left, & on the right 30/5= 6. So, x=6.
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Step 1: 5x=30
Step 2: 5x/5=30/5 (the 5s cancel out, leaving you just x on the left)
Step 3: x=6
Part B : This solution will have only 1 answer, & that answer is 6. -6 wouldn't be counted as one because if you plug -6 into the equation as x, the sides won't equal, you'll have -30=30 which isn't true.
Hope this makes sense & helps you ! (:
