Respuesta :

2.8-(-5.1)

-(-5.1)=5.1

2.8+5.1= 7.9

Is this what you were asking?

Subtracting means adding the opposite.Subtracting -5.1 means adding the opposite of -5.1 which is +5.1.
2.8 - (-5.1) = 2.8 + (+5.1) = 2.8 + 5.1 = 7.9