Multiply the first equation by 2
2x + 2y =30
now we’ll add the second equation to the first equation
2x + 2y =30
-2x+5y= -2
7y=28
divide by 7
y=4
now plug y back into the first equation
x + 4 = 15
subtract 4
x=11
A. Is the attached image. The slope is 7.5x
b. 1 = 7.5x
x = 1.33333…
This is hours so we must multiply this by 60
x = 8 min
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 don’t see the problems you want me to solve. Sorry