onclick start and stop the count react

1class Controls extends React.Component{
2    state={
3        myInterval : null,
4        time: 25*60*1000
5    }
6    countDown = () => {
7        this.setState({
8            time : this.state.time-1000,
9        })
10    }
11    startTimer = () => {
12        this.setState({myInterval : setInterval(this.countDown,1000)})
13    }
14    stopTimer = () => {
15        clearInterval(this.state.myInterval)
16    }
17    render(){
18        return(
19            <div>
20                <button onClick={this.startTimer}>Start</button>
21                <button onClick={this.stopTimer}>Stop</button>
22                {this.state.time}
23            </div>
24        )
25    }
26}
27
28
29class App extends React.Component{
30    render(){
31        return <Controls/>
32    }
33}
34
35
36
37
38
39ReactDOM.render(
40  <App />,
41  document.getElementById("react")
42);