Explications étape par étape:

a) Currency exchange office 1:

Amount in pounds = n * 0.87

Currency exchange office 2:

Amount in pounds = n * 0.81

b) For Anne exchanging 100€:

Office 1: Amount in pounds = 100 * 0.87 = 87 pounds

Office 2: Amount in pounds = 100 * 0.81 = 81 pounds

Since office 1 gives a better rate, I would recommend Anne uses office 1.

For Rose exchanging 40€:

Office 1: Amount in pounds = 40 * 0.87 = 34.8 pounds

Office 2: Amount in pounds = 40 * 0.81 = 32.4 pounds

Although office 1 gives a slightly better rate, the 4 pound commission would negate this. Therefore I would recommend Rose uses office 2 with no commission.