The Command "grunt" exited with code 3 error when building project

I am unfamiliar with Grunt and I tried to follow steps to install it. I am getting this error and I have tried for a week to get it to work. Can anyone please help me. I am an undergrad student and don't have that much know how with it. I followed the installation instructions on the website. and know its a task error. but after that I cant find any working solutions.