Cannot determine which native SDK version your project uses because the module `expo` is not installed. Please install it with `yarn add expo` and try again.

I am new to React-Native and Expo. I executed the " Setting up the development environment" commands , and get error when trying expo start :

Cannot determine which native SDK version your project uses because the module `expo` is not installed. Please install it with `yarn add expo` and try again.
    ├─ getExpoSDKVersion C:\Users\boulanger\AppData\Roaming\npm\node_modules\expo-cli\node_modules\@expo\config\src\Project.ts:23:9
    ├─ ensureConfigHasDefaultValues C:\Users\boulanger\AppData\Roaming\npm\node_modules\expo-cli\node_modules\@expo\config\src\Config.ts:478:18
    ├─ fillAndReturnConfig C:\Users\boulanger\AppData\Roaming\npm\node_modules\expo-cli\node_modules\@expo\config\src\Config.ts:103:10
    ├─ getConfig C:\Users\boulanger\AppData\Roaming\npm\node_modules\expo-cli\node_modules\@expo\config\src\Config.ts:179:10
    ├─ C:\Users\boulanger\AppData\Roaming\npm\node_modules\expo-cli\src\commands\utils\profileMethod.ts:16:21
    ├─ action C:\Users\boulanger\AppData\Roaming\npm\node_modules\expo-cli\src\commands\start.ts:29:24
    ├─ C:\Users\boulanger\AppData\Roaming\npm\node_modules\expo-cli\src\commands\start.ts:124:22
    └─ expo start C:\Users\boulanger\AppData\Roaming\npm\node_modules\expo-cli\src\exp.ts:349:7

expo diagnostics output:

Expo CLI 4.3.2 environment info:
    System:
      OS: Windows 10 10.0.19042
    Binaries:
      Node: 14.16.0 - C:\Program Files\nodejs\node.EXE
      npm: 7.7.4 - C:\Program Files\nodejs\npm.CMD
    IDEs:
      Android Studio: Version  4.1.0.0 AI-201.8743.12.41.7042882
    Expo Workflow: managed

what should i do ?

is expo installed? If not, you should follow the suggestion in the error message and run yarn add expo