Question

Don’t know how to work them

Answer 1

a positive multiplied by a negative is a negative:
2.5+(-7.9)=2.5-7.9

and negative times a negative is a poisitive:
3.7-(-12.4)=3.7+12.4

for fractions if you have mixed numbers you multiply that big number by the denomintator and add it with the numberator:
$20 \frac{5}{16}$ =[(20x16)+5]/16