Bonjour !
1- <em>Nous "avoir" de la chance</em>
Nous avons de la chance.
<em>AVOIR présent</em>
j'ai
tu as
il/elle/on a
nous avons
Vous avez
ils/elles ont
-
2- <em>Nous sommes "malade"</em>
<em> </em>Nous sommes <u>malades</u>.
<em>the adjective here is called "attribut du sujet". it doesn't come before or after a noun (adjectif épithète) but after a verb. They agree as well with the subject. Nous (plural) + malades (plural) </em>
<em>-</em>
3- Inc<em>orrect sentence</em>
Il <u>est</u> 20 ans. ► Il a 20 ans => correct
<em>In English "to be x years old". In French you always use "avoir".</em>
<em> Subject + avoir + ? ans.</em>
<em>-</em>
4- <em>Masculine form of "Elles sont blondes"</em>
<em> </em>Ils sont blonds
<em>As in n° 2, the adjective agrees with the subject. </em>
<em> ils (masculine plural) + blonds (masculine plural)</em>
<em>-</em>
Hope this helps to understand better ☺☺☺
<em> </em>
-