What is the value of $a$?

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For a particular car, the linear function

f

gives the predicted power, in brake horsepower (bhp), for engine speeds between 1,000 revolutions per minute (rpm) and 6,000 rpm. According to this function, the car's predicted power is 600 bhp at an engine speed of 4,500 rpm. The equation

f (x) = \frac{1}{7} (x - a) + 228

defines

f

, where

x

is the engine speed, in rpm, and

a

is a constant.

What is the value of

a

1896