Note the equal sign, what you do to one side, you do to the other side. Isolate the variable z.
First, subtract 3z and add 6/4 to both sides
4z (-3z) - 6/4 (+6/4) = 3z (-3z) + 1 (+6/4)
4z - 3z = 1 + 6/4
Simplify. Note that 1 = 4/4.
z = 4/4 + 6/4
Simplify. Combine like terms
z = 10/4
Simplify. Change the improper fraction into mixed fraction and simplify.
z = 10/4 = 2 2/4 = 2 1/2
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