Weighted averages?

Question

I didnt have time to go to tutorials in school today so here are two questions that I can't seem to understand, I need an explanation.

A car radiator has a capacity of 16 quarts and is filled with a 25% antifreeze solution. How much must be drained off and replaced with pure antifreeze to obtain a 40% antifreeze solution?

and...

An express train travels 80km per hour from ironton to wildwood. A local train, traveling at 48km per hour, takes 2 hours longer for the same trip. How far apart are ironton and wildwood?

Answer 1

The goal would be to have:

40% (16 quarts) = 6.4 quarts antifreeze.

if x is the amount to be drained and replaced with 100% antifreeze, then:

100%x + 25%(16-x) = 6.4
.1x + 4 - .25x = 6.4
.75x = 2.4
x = 3.2 quarts to be drained and replaced with 100% antifreeze.

Distances are the same so

r1t1 = r2t2
80t = 48(t + 2)
80t = 48t + 96
32t = 96
t = 3 hours for the faster train to get there, so the distance must be:

3(80) = 240 km.

Answer 2

i don't know about the first one.
but, second one
80x=48(x+2)
80x=48x+96
32x=96
x=3
it takes 3 hours for express train to travel

so, 3x80=240km apart