Hi there!
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I believe your answer is:
[tex]p =\frac{q-5r}{2}[/tex]
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Here’s why:
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[tex]\boxed{\text{Solving for 'p'...}}\\\\2p+5r=q\\-----------\\\\\rightarrow 2p + 5r - 5r = q - 5r\\\\\rightarrow 2p = q - 5r\\\\\rightarrow \frac{2p=q-5r}{2}\\\\\rightarrow \boxed{p =\frac{q-5r}{2}}[/tex]
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Hope this helps you. I apologize if it’s incorrect.