Chapter 8 Rational Functions - Mixed Review of Problem Solving - Lessons 8.1-8.3 - Page 572: 7

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Given $I=\frac{a}{d^2}$ where $a$ is a constant. We know $I=10\frac{W}{m^2}$ when $d=1$ Substitute $a=Id^2=10\frac{W}{m^2}(1m)^2=10W$ Substituting $d=15$, we have $I=\frac{10W}{(15)^2}=\frac{2}{45}\approx0.04W$