Solve for z
z=7
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90=15\left(z-1\right)
Variable z cannot be equal to 1 since division by zero is not defined. Multiply both sides of the equation by z-1.
90=15z-15
Use the distributive property to multiply 15 by z-1.
15z-15=90
Swap sides so that all variable terms are on the left hand side.
15z=90+15
Add 15 to both sides.
15z=105
Add 90 and 15 to get 105.
z=\frac{105}{15}
Divide both sides by 15.
z=7
Divide 105 by 15 to get 7.
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