There's no need to convert to km/h ...1 knot is 1 nautical mile per hour and the answers (multiple choice) will be given in nm.
The formula, where x is the time taken is
175x = 235(x-0.75). where 0.75 = 45 minutes time difference.
x = 2.9375 = 2 hours, 56 mins and 25 seconds. They will meet at 12:56 - just in time for lunch. Once you've got this, the distance should be easy.
This is a typical test question and if you have problems manipulating these formulae, you may want to seek a bit of one to one tuition.
Cheers
Whirls