DISTANCE RATE TIME HELP!! Please help me!!!!!?

Question

my grade nine D=RT problem:
a jet flew from Toronto to Paris at 800 km/h and returned at 700km/h. if the total trip, not including stopover time, took 15 h, how far is it from Toronto to Paris.
I need help forming the actual algebraic expression
i don't need the answer just help with the theory
usually, it's "if a jet took 10 hours, at 100 km/h, how far did it go", but this is different and i'm EXTREMELY unsure on how to solve it

Answer 1

speed , s1 = 800 km / h
speed , s2 = 700 km / h
distance = d km

time , t1 = d / 800 h
time , t2 = d / 700 h

d / 800 + d / 700 = 15
700 d + 800 d = (15) (800) (700)
1500 d = (15) (800) (700)
1500 d = (1500) ( 8 ) (700)
d = 5600

5600 km from Toronto to Paris.

Answer 2

let x be the time it takes to go from toronto to paris
distance = 800x
on return it takes 15-x
distance = 700(15-x)
so eq. 800x=700(15-x)
800x = 10500-700x
1500x=10500
x = 7
distance = 800x7 = 5600 km