This is all I can do for now, I might be back to solve the rest, I’m sorry.
It will take the seal 6.5 hours to swim 52 miles.
4x / 5 = 1 / 3 ( 2x - 15 )
4x / 5= ( 2x - 15 ) / 3
4x × 3 = 5 ( 2x - 15 )
12x = 10x - 75
12x - 10x = - 75
2x = - 75
x = - 75 / 2
x = - 37.5
I think the answer is 52 cm. If you add all the numbers and find out the two missing numbers you will get 52. ( if I’m sorry so how, I’m sorry :))