The most appropriate real-world problem that models the equation \(0.08x = 0.06x + 140\) is:
A certain sum yields $140 more in interest when the interest rate is 8% than when it is 6%.
In this context, \(x\) would represent the principal amount (the certain sum), \(0.08x\) is the interest earned at 8%, and \(0.06x\) is the interest earned at 6%. The equation states that the difference between the two interest amounts is $140, which aligns with the modeling of the equation.