In the expression x(s - 4) + yb, x is a coefficient.
A coefficient is a number that multiplies a variable or a product of variables. In this case, x is being multiplied by the quantity (s-4), so it is a coefficient.
The other terms in the expression are y, b, s, and 4. y and b are also coefficients, but they are written next to each other to form a product. s and 4 are constants, which means they are fixed values and don't change.