I'm pretty sure the answer is indigo. If I'm wrong then I apologize.
In the year between 1760 and 1840 AD a tremendous change occured in the field of industry in England .Different machines were invented and came into use to produce the goods . Such machines were operated by power and produced the goods many times more than the goods produced by hands .These change occured in England is called Industrial Revolution
Solve for one of the variables first ,, then whatever answer you receive from x or y , you then begin to plug it in to get other variable.