Please help images



I need a signage banner printed - size: 30 inches x 70 inches at 300 dpi

I would like to purchase the images myself to avoid copyright related problems. I will be using Shutterstock fyi.

My preferences regarding the design:
Size: 30 inches x 70 inches
DPI: 300
Header portion: The image (that I will provide) should cover 50% of the banner.

Please let me know the image size in pixels.

Thank you