Solar Storms, nasty events originating with the sun where use clouds of magnetized clouds of ionized gas

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Solar Storms, nasty events originating with the sun where use clouds of magnetized clouds of ionized gas (a plasma) are ejected from the sun's atmosphere (called a Corona Mass Ejection, a CME), can wreak havoc on different objects in the solar system. CMEs can be as large as 1 and a half trillion tons of gas, and travel at 3 million miles per hour. This sounds incredibly fast, but over the vast reaches of our solar system, it can take many hours to reach our chosen planetary body. When these CMEs hit the Earth's magnetosphere, they can disrupt satellite communications, and electrical power grids, and causes Auroras. Not all of the planetary bodies in our solar system have a magnetic field though, and CMEs are a big concern with the prospects of establishing a human colony on Mars for example. When NASA was monitoring CMEs with their STEREO spacecraft they observed that it took 70 hours to reach Earth. Using this information, set up an equation to determine how much time it will take to reach your planetary body (Pluto).
Explain the equation that you set up for your calculation.