Which expression means 3 times a number h

This basically means 3 × h, so the answer is 3h when simplified.

3xh is the same thing as 3•h so all u have to do is simplify it and your answer is 3h

For 15 to 20, change the equation from y=mx+b into mx-y=-b
Example: 15) y=-5x+2 into -2=-5x-y or 2=5x+y
For 21-29, the numbers in the parenthesis are coordinates (x, y) so uh the equation y=mx+b plug in the m that is given and x and y and then solve for b to complete the equation
Ex: 21) (-8,3) m=2
Y=mx+b
3=2(3)+b
3=6+b
-3=b
So y=2x-3
Do the same to the others