$2pq$ and $-7qp$ are like terms.

When $y=-1$, the value of the expression $2y-1$ is $3$

Write the variables, constants and terms of the following expression.

$18+x-y$

Write the variables, constants and terms of the following expression.

$7p-4q+5$

Write the variables, constants and terms of the following expression.

$29x+13y$

Write the variables, constants and terms of the following expression.

$b+2$

If $x=2$ and $y=3$, then find the value of the following expression.

$2x-3y$