1) -15+4r=-9
-15+4r=-9
We move all terms to the left:
-15+4r-(-9)=0
We add all the numbers together, and all the variables
4r-6=0
We move all terms containing r to the left, all other terms to the right
4r=6
r=6/4
r=1+1/2
2) 5-y/3=-1
5-y/3=-1
We move all terms to the left:
5-y/3-(-1)=0
We add all the numbers together, and all the variables
-y/3+6=0
We multiply all the terms by the denominator
-y+6*3=0
We add all the numbers together, and all the variables
-1y+18=0
We move all terms containing y to the left, all other terms to the right
-y=-18
y=-18/-1
y=+18
3) 42=-5x-8
42=-5x-8
We move all terms to the left:
42-(-5x-8)=0
We get rid of parentheses
5x+8+42=0
We add all the numbers together, and all the variables
5x+50=0
We move all terms containing x to the left, all other terms to the right
5x=-50
x=-50/5
x=-10