First, define what is a constant and a coefficient.
Constant = Is a number on its own, or sometimes a letter such as a, b or c to stand for a fixed number.
Coefficient = Is a number used to multiply a variable, for example 6x, 8x, or 5y, also sometimes a letter if it is accompanied by a variable example bx.
In this expression, b and 4 are constants. And 5 is a coefficient because it is accompanied by y.
Jake missed b as a constant.