Equation #1:
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
Equation #2:
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
Equation #3:
Simplifying
42 = 5x + -8
Reorder the terms:
42 = -8 + 5x
Solving
42 = -8 + 5x
Solving for variable 'x'.
Move all terms containing x to the left, all other terms to the right.
Add '-5x' to each side of the equation.
42 + -5x = -8 + 5x + -5x
Combine like terms: 5x + -5x = 0
42 + -5x = -8 + 0
42 + -5x = -8
Add '-42' to each side of the equation.
42 + -42 + -5x = -8 + -42
Combine like terms: 42 + -42 = 0
0 + -5x = -8 + -42
-5x = -8 + -42
Combine like terms: -8 + -42 = -50
-5x = -50
Divide each side by '-5'.
x = 10
Simplifying
x = 10
