Nouns ending in -as are masculine.
Is tas masculine or feminine?
letas
The rule behind it
100% of -as nouns are masculine
In context
J'ai un tas de problèmes à résoudre.
I have a lot of problems to solve.
Nous sommes confrontés à un tas de problèmes.
We are faced with a host of problems.
Ça m'est arrivé des tas de fois.
That's happened to me plenty of times.