simplify-calculator
solve for u, \left(\left(\left(\frac{p}{a}+\frac{u}{e}\right)\cdot\left(\left(\frac{\left(p+u\right)}{\left(\frac{p}{a}+\frac{u}{e}\right)}\right)-n\right)\right)- \left(\left(\frac{p}{a}+\frac{u}{e}\right)\cdot\left(\frac{\left(p+u\right)}{\left(\frac{p}{a}+\frac{u}{e}\right)}\right)\cdot m\right) - \left(\left(\frac{p}{a}+\frac{u}{e}\right)\cdot n\cdot m\right) \right)=-f
en