Question

x+3.1=2.6
x=

Answer 1

Well.. if
\[x + a = b\]
Then
\[x = b - a\]

Answer 2

if x+3.1=2.6
it is the same as x+3.1-3.1=2.6-3.1
therefore x= -1.5

Answer 3

-0.5