4, 7 and 9 are mutually coprime, so you can use the Chinese remainder theorem.
Start with

Taken mod 4, the last two terms vanish and we're left with

We have
, so we can multiply the first term by 3 to guarantee that we end up with 1 mod 4.

Taken mod 7, the first and last terms vanish and we're left with

which is what we want, so no adjustments needed here.

Taken mod 9, the first two terms vanish and we're left with

so we don't need to make any adjustments here, and we end up with
.
By the Chinese remainder theorem, we find that any
such that

is a solution to this system, i.e.
for any integer
, the smallest and positive of which is 149.
I used a converter so i put 3200 meters into feet which was 10,498.69 and i rounded it to 10,498 and then i subtract 10,498 feet from 11,808 feet and got 1,310 feet as the answer
This is a one-step equation. All you need to do is multiply the 2.5 over to the 20 to get x by itself.
x=50
Hope this helps!