Unwanted solutions

How many solutions in $\Z_{27}$ does $12x \equiv 13 \pmod {27}$ have?
How many solutions in $\Z_{27}$ does $12x \equiv 21 \pmod {27}$ have?
How many solutions in $\Z_{27}$ does $16x \equiv -1 \pmod {27}$ have?
How many solutions in $\Z_{100}$ does $30x \equiv 20 \pmod {100}$ have?
Submit the numbers separated by space.