a. 

`|x + 2019| + |2020 + x| + |2021 + x| = 13x`

`=> 3x + 6060 = 1`

b. 

`(1/2)^x+1 + (1/2)^x+2 = 3/64`

`=> 1/ 2^x+1 + 1/ 2^x+2 = 3/64`

`=> 3/ 2^x+2 = 3/64`

`=> 2^x+2 = 64 = 2^6`

`=> x + 2 = 6`

`=> x =4`