Hello, To solve this problem you must write an equation.
Petra=P and Petra's Mother=2p+12 so:

First add the like terms: 

Now you have:
 
Subtract 12 from both sides of the equation.
 +12 & -12 cancel out.
You are left with:
 divide by 3
. P=11
We already know Petra is 11 yrs. old. To find out Petra's mother's age go to the original equation and plug in the solutions.
Petra's Mother=2p+12
 
First multiply:
 
Now you have: 22+12
 
Petra's Mother is 34 yr. old.
TO CHECK YOUR ANSWER:
 
Restate Original equation:

Now plug in the number:
 
Solve this problem like a normal equation.
First multiply:
 
Now you have: 
 
continue to add the numbers:
 when both sides of the equation are equal the answer is correct.
Hope you can understand this problem better now! If you have any questions e-mail me Southqueensb@yahoo.com
~EVY~