Find the coefficient of $xy$ in the expression $2x^{2}y+4xy-3yx$.

Are the terms $\frac{2}{5}{x}^{2}y, \frac{-3}{2}{x}^{2}y$ and $\frac{10}{7}{x}^{2}y$ like terms?

Is $7x^2-9x-3\left(-3x^2-3x+2\right)$ a monomial or a binomial?

What is the constant term in the sum of $\left(5x^2-7x+4\right)$ and $\left(7x-8\right)$?

If $a=2, b=-1$, then find the value of $a^2+b^2+2ab$.