Please explain this algebra as I have failed to understand it, thanks

Note that the units in which consumption goods are measured are subject to the standard rules of arithmetic. For example, when we simplify the expression on the right-hand side of the equation M/PS = (100/wk) + (5/sq. m), we are essentially dividing one fraction by another, so we follow the standard rule of inverting the fraction in the denominator and multiplying it by the fraction in the numerator: (sq. m/5) X (100/wk) = (100 >