



 
Kimberley, Let's do it first with specific numbers for t, b, r and c and then see if we can mimic the steps when these variables don't have specific values.
I would first add 3a to both sides to get
and rearrange to get
Next add 7 to each side and also notice that 5a and 3a have a common factor of a. Thus the equation becomes
Since I have specific numeric values I can perform he arithmetic to get
Finally divide both sides by 2 to get the answer
Ok, now back to the original problem.
The first step is to add ar to both sides.
Again a rearrangement gives
Notice here that at and ar have a common factor of a. Complete the solution mimicking the steps above and let me know what you get for a. Penny  


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