Wx+yz=bc
minus wx on both sides
yz=bc-wx
dividing 'y' on both sides
Hence,
z=(bc-wx)/y
Here is what you need.
Hope it helped
10. Infinitely many solutions:

Simplify this equation:

When
the equation becomes

This equality is true for all x, thus the equation has infinitely many solutions.
11. The equation
should have one solution x=-1.
First, simplify the equation:

This equation will have solution x=-1 when

Therefore, the initial equation is

12. The equation
should have infinitely many solutions.
Simplify it:

When
this equation will have infinitely many solutions.
There are 23 nickles in her purse
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