You should colspan attribute and input element at right place as follows:
<!-- All the best -->
<!DOCTYPE html>
<html>
<head>
<title>
</title>
</head>
<body>
<table border="1px" width="75%">
<tr height="50px">
<td colspan="4">
<input type="text" style="width: 95%; height: 50px;">
</td>
</tr>
<tr height="50px">
<td></td>
<td></td>
<td></td>
<td></td>
</tr>
</table>
</body>
</html>