Here is how it is coded.
$meta_query = array(
'relation' => 'AND',
array(
'key' => 'minimum_loan_amount',
'value' => $loan_amount_requested,
'type' => 'numeric',
'compare' => '>='
),
array(
'key' => 'maximum_loan_amount',
'value' => $loan_amount_requested,
'type' => 'numeric',
'compare' => '<='
)
);