First Order Differential Equation for Mixture Problem

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Homework Statement


\frac{dA}{dt}=\frac{5}{3} - \frac{4A}{150+2.5t} lb/min
so basically dA/dt = rate in - rate out

Homework Equations


This is basically a mixture problem. There is 10 gals/min going in and 4gals/min going out. Tank starts at 150/300 gallons with 1/4 lb/gal mixture. 5gal/min are coming in at 1/3 lb/gal mixture, other 5 is clean water.

The Attempt at a Solution


Derived this equation, tried to manipulate it algebraically, but not really sure how to proceed. Can't seem to separate the equation and integrate, all I really know is integration factors and substitution. Any help would be great. Thanks.
 
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Nevermind, got it using integration factor.
 
There are two things I don't understand about this problem. First, when finding the nth root of a number, there should in theory be n solutions. However, the formula produces n+1 roots. Here is how. The first root is simply ##\left(r\right)^{\left(\frac{1}{n}\right)}##. Then you multiply this first root by n additional expressions given by the formula, as you go through k=0,1,...n-1. So you end up with n+1 roots, which cannot be correct. Let me illustrate what I mean. For this...
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