how can you tell what dpi an image is on the adobe stock images

See screenshot below:

Dots per inch (DPI) is a print concept that has no relevance to digital artwork. 

Image previews are displayed at the web standard for browsers which is 96 pixels per inch (PPI). 

Full-sized downloads vary by the total number of pixels (height x width). More pixels produce higher-res images. Fewer pixels produce lower-res images. 

Re-scaled RASTERS are subject to pixelation. If you’re working on big projects for print, search Stock for resolution-independent VECTORS (AI, EPS or SVG) which can be re-scaled in Illustrator to any size the customer requires without quality loss. 

Hope that helps.

You can divide the number of pixels by 300. E.g., 6000 px / 300 = 20 inches, and 3375 px / 300 = 11.25 inches. This will at least tell you if the image meets your needs in terms of it actual dimensions. 

Hello,

DPI (Dots per inch) is important when you want to print. You can choose the DPI value when you want to print. The DPI value on screen does not apply. On screen it is about pixels. (PPI - Pixels per inch.)

You cannot check the resolution (DPI) until you purchase the item.
Since the DPI setting can be changed later, please calculate the effective DPI based on the pixel count and your intended usage size.
DPI is not particularly important.