V=lwh solve for l in literal equations

Basically, you just perform whatever operations are needed to get the variable you DON'T know by itself on one side of the equal sign, plug in the variables you do know, and you have it. In your example, say you don't know the length, but you know the others:
V = l*w*h
V/w*h = l*w*h/w*h
V/wh = l
Now l is by itself, so you can substitute values for the other variables and solve for l.

Y= -2x-1 the negative in front of the 2 is because the slope is negative and the -1 is because it’s down 1 on the y axis.