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The thin lens equation 1/f = 1/do + 1/di ties focal length to the object and image positions. An object 0.3 m out imaged at 0.15 m implies a 0.1 m focal length, or 10 dioptres. The magnification is -di/do, so this arrangement gives a real, inverted image half the object's size.
Thin lens equation
1/f = 1/do + 1/di
Magnification
m = -di / do
The image is inverted. Real images from converging lenses always are, which is why a camera sensor sees an upside-down image.
At the focal point. As do tends to infinity the 1/do term vanishes and di becomes f.