Wait I will figure out.
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Okay, distribute the integrating factor on the left, and you will find the LHS can then be expressed as the derivative of the product of the integrating factor and the dependent variable r. This is the reason for computing the integrating factor in the first place.
You should really be starting new threads for new questions, and looking into using $\displaystyle \LaTeX$ to post your math instead of images (frequently sideways) of handwritten work.
We are given:
$\displaystyle (x+y)dx+(3x^2-y)dy=0$
Is this ODE exact?