I won't answer them all for you (don't want to cheat - need to learn something). But for the first one given:
<span>-2x-9y=-25 -4x-9y=-23
you set up either x or y (which ever one you want to eliminate) so that one of them cancels. So this one is easy - you just have to multiply an entire row by negative (doesn't matter which one) - so that the y's will be + and -
Since they're both 9 and they're subracting NOW - you can eliminate the y value. Now add/subtract the x's. So it'd be -2 or 2 depending on how you eliminated y. Then add the number outside of the = sign. Now just solve for x. After that plug in whatever you got for x into both of the rows. Then find the y value.
Hopefully this wasn't confusing -- reply if it is and I will try to simplify. I can give you contact if you need help with the rest
A) It says in fraction form. y=5/4x +15 b) it says it should be a decimal. If you extend the line, it will reach 15.5 hours. c) I think your answer was correct