calculați:
a)3+6+9+12+...+2019
c)5+10+15+20+...+2020
b)4+8+12+...+2020
d)7+14+21+...+2023
am nevoie de ex plssss
![Calculația369122019c51015202020b48122020d714212023am Nevoie De Ex Plssss class=](https://ro-static.z-dn.net/files/d22/7f12b2eb224bb2a0476b71a2f32d9a75.jpg)