I am supposed to simplify 1/a-b - 1/b-a

The answer is 2/ a-b

But I don't know how they got the denominator during the working and the final answer.
Please help, thank you

5=812a+9+3

step 1: simplify both sides of the equation.

5=812a+9+3

5=(812a)+(9+3)(combine like terms)

5=812a+12

5=812a+12

step 2: flip the equation.

812a+12=5

step 3: subtract 12 from both sides.

812a+12−12=5−12

812a=−7

step 4: divide both sides by 812.

812a /812 = -7/812

a= -1/116

so the answer is

a=   -1/116

2.14x - 12.18 = -5.76

add 12.18 to each side

2.14x -12.18 +12.18 = -5.76 +12.18

2.14 x =6.42

divide by 2.14

2.14x/2.14 = 6.42/2.14

x=3