let's call the number x, so:
twice a number minus 3 is 27 can be written as:
[tex]2\cdot x-3=27[/tex]
Adding 3 on both sides:
[tex]\begin{gathered} (2\cdot x)-3+3=27+3 \\ 2\cdot x\text{ = 30} \end{gathered}[/tex]
dividing by 2 on both sides:
[tex]\begin{gathered} \frac{2\cdot x}{2}=\frac{30}{2} \\ x=15 \end{gathered}[/tex]
The number is 15.
