Rationalize and simplify square root of 5m over square root of 5n

√5m/√5n 
so here you have to rationalize it by making the denominator not a root. and to do that the easiest way is to multiply it by itself.
*but when you multiply you multiply it to both numerator and denominator
√5m×√5n÷√5n×√5n
then multiply
√25mn÷√25n^2
√5·5·m·n/√5·5·n·n
then simplify
5√mn/5n
√mn/n

It is going to be the third choice

Yes you do, so £1973.09 - £1473.50 = £499.59 so tim overpaid £499.59 .hope this ; )