Photo resolution vs size

[Blighty]

It is best to think in pixels.

You say your camera takes photos 19x25 @ 76dpi
That is (19x76)x(25x76) pixels
=1444x1900 pixels

For a 5x7 print at 300dpi you need
(5x300)x(7x300) pixels
=1500x2100 pixels
Crop, keeping the aspect ratio at 1500x2100
Then scale to 1500x2100 if necessary