Just had to count tips at work and couldn't do basic addition im mortified

I just cried on the bus because I had to count and add tips at work so I split them with another girl to help her and i just couldn't do it, it was so easy as well and she finished in two minutes and I was counting on my hands like an idiot someone else had to do it for me im so embarrassed and so pissed I never even learned basic maths