Put the numbers in the given equation and solve for k.
... $11 = k·(8 €)
Divide by the coefficient of k:
... k = $11/(8 €) = 1.375 $/€
Then your equation is ...
... y = (1.375 $/€)x
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It is fairly common to leave the units out of such equations, assuming that everyone understands that x is in euros and y is in dollars and the conversion factor includes a unit change from euros to dollars. Thus, you might expect to see ...
... y = 1.375·x
