A taxi company charges a fixed hire fee (which is a whole number of dollars) plus a rate for each
kilometer (which is a multiple of 10¢ and more than the set national minimum rate of $1.75),
rounded up to the nearest kilometer.
Maira’s last journey cost $37.90, but she does not know how far it was, or what the fixed hire fee
is. She wants to know how far the journey was.

She has a previous bill from the same taxi company, for a different journey, for $21.80.
How far was her last journey?