JSFiddle - React, Tailwind, and code Playground

HTML

<script src="https://ajax.googleapis.com/ajax/libs/angularjs/1.3.0/angular.min.js"></script>
<div ng-app="myapp">
    <fieldset ng-controller="FirstCtrl">
        <select
                ng-options="p.first + ' x ' + p.last for p in people"
                ng-model="selectedPerson"></select>

        {{ selectedPerson.first }} x {{ selectedPerson.last }}
    </fieldset>

    <div class="box" ng-style="{'width' : selectedPerson.first}">

    </div>
</div>

CSS

.box
        {
            background: red;
            width:200px;
            height:200px;
        }

JavaScript

var myapp = angular.module('myapp', []);
myapp.controller('FirstCtrl', function ($scope) {
    $scope.people = [
        { id: 1, first: 100, last: 200 },
        { id: 2, first: 200, last: 300 },
        { id: 3, first: 300, last: 400 },
        { id: 4, first: 400, last: 500 }
    ];
});