Show amount for 3, 6 and 12 installments (with percentage fee), under regular price

mx_price_per_installments_w_fee.php

add_action( 'woocommerce_single_product_summary', 'mx_price_per_installments_w_fee', 11 );

function mx_price_per_installments_w_fee() {

    global $product;
    $price = $product->get_price();
    $threeinstallments = 3;
    $sixinstallments = 6;
    $twelveinstallments = 12;
    $fee = (3.5/100) * $price;
    $price4installments = $price + $fee;

    $price_per_threemonths = round ($price4installments / $threeinstallments, wc_get_price_decimals(), PHP_ROUND_HALF_DOWN);
    $price_per_sixmonths = round ($price4installments / $sixinstallments, wc_get_price_decimals(), PHP_ROUND_HALF_DOWN);
    $price_per_twelvemonths = round ($price4installments/ $twelveinstallments, wc_get_price_decimals(), PHP_ROUND_HALF_DOWN);

    echo "
    <div id='installments-container'>
        <div id='installments-text'>
		Obročno plaćanje: 3 x <span>". $price_per_threemonths ." Kn</span> | 6 x <span>". $price_per_sixmonths ." Kn</span> | 12x <span>". $price_per_twelvemonths ." Kn</span>
        </div>
    </div>
    ";
}