Idon’t know whether to add or subtract in word problems with fractions me

Expresa commuter train leaves downtown sation and travels at a average speed of 55 miles per hour towards the north side sation, which is 50miles away. thirty minutes later, express commuter train #7 leaves north side and travels at a average speed of 35miles per hour towards downtown sation. at the moment the two trains pass each other, how far(in miles) is train #12 from the downtown sation and how long(in minutes) has the #12 train been traveling

The value of the expression 16-^3/4 8 1/8 -6 6 1/40 1/64

Iknow its nothing to do with education, but what type of thing should i wrote here? ? : ) its for mcdonald's btw.