Argument #2 is not an array
When you are going to apply an and in your relatedTo in Craft 3 it expects the following arguments to be arrays with the structure like here 

{% set entries = craft
    .entries
    .section('institutions')
    .relatedTo(['and', 
        {element: state}, // &lt;- or targetElement / sourceElement
        {element: solution}
    ])
    .limit(4) 
    .all()
%}