Write an expression to represent:
                    CardinalThrough20(-B) less than the product of cardinalThrough20(M) and a number x.
                
M * x + B
                        The product of cardinalThrough20(M) and a number x can be written as
                        Mx.
                    
CardinalThrough20(-B) less than something means that we subtract -B from it.
                        If we subtract -B from expr(["*", M, "x"]), we have expr(["+", ["*", M, "x"], B]).
                    
                    CardinalThrough20(B) more than the product of cardinalThrough20(M) and a number x.
                
                        The product of cardinalThrough20(M) and a number x can be written as
                        Mx.
                    
CardinalThrough20(B) more than something means that we add B to it.
                        If we add B to expr(["*", M, "x"]), we have expr(["+", B, ["*", M, "x"]]).
                    
                    CardinalThrough20(B) minus the product of cardinalThrough20(-M) and a number x.
                
                        The product of cardinalThrough20(-M) and a number x can be written as
                        -Mx.
                    
CardinalThrough20(B) minus something means that we subtract it from B.
                        If we subtract expr(["*", -M, "x"]) from B, we have expr(["+", B, ["*", M, "x"]]).
                    
                    The sum of cardinalThrough20(B) and the product of cardinalThrough20(M) and a number x.
                
                        The product of cardinalThrough20(M) and a number x can be written as
                        Mx.
                    
"Sum" means that we add B and expr(["*", M, "x"]).
If we add B and expr(["*", M, "x"]), we have expr(["+", B, ["*", M, "x"]]).