Npm ls gives error for unmet peerDependencies

I am having an issue of peerDeps.

My app has package.json
devDependencies: {
a : 1.0.0,
b: 2.0.0
now ‘a’ has in its package.json
eslint: ^7.12.1

and ‘b’ has in its package.json
devDependency: {
eslint: 6.8.0

now i see in My apps node_modules: eslint@6.8.0 being installed
now when npm i is done it gives warning of missing peerDepds : eslint@^7.12.1

But my script also has npm ls which gives error of npm ERR! peer dep missing: eslint@^7.5.0

I tried putting eslint@7.5.0 in devDeps in my apps package.json…But that also gives error. npx ncu fails after i do this.

How can i resolve this. Can you please help me withh this. Thanks!