Area bounded by these lines and curves

[Reshma]

Find the area of a figure bounded by the equilateral hyperbola xy = a^2, the x-axis, and the lines x = a, b = 2a.

My work:
The equations of the lines and curves involved here are:
xy = a^2
y = 0
x = a
I don't know how b=2a is treated as an equation of a line here & hence I am puzzled as how to get the limits for the definite integral here. Well the formula I tried using is(Q stands for area):
Q = \int_a^b [f_1(x) - f_2(x)]dx

Guidance needed.

 

[neutrino]

I guess it's a typo. It's probably x = 2a.

 

[Reshma]

I guess it's a typo. It's probably x = 2a.

Thanks, you are right!
y = {a^2\over x}
Q = \int_a^{2a} {a^2\over x} = a^2\ln 2

...which tallies with the solution given .