We know that formula for the area of the circle is \pi r^2 and this area is equal to 49.
We can make such equation
\pi r^2=49
For simplification we canassume pi=3
3r^2=49 /:3 divide both sides by 3
r^2=16.3 \sqrt{both sides}
r= \sqrt{16.3}
r=4.04
We know that diameter is equal 2 times radius, so diameter=2*4.04=8.08 - its the answer