I need a answer for this problem

The answer would be f(x)=3.9n+15.85 since every floor is 3.9 meters high you need to multiply 3.9 by the number of floors which in this case would be n. Then you add the height of the antenna because it is included in the measurement. Using the order of operations you would multiply from right to left first which would give you the height of the building without the antenna, then you would add the 15.85 which would give you the total height of the building including the antenna if you would know how many floors there are.

So radio antena is 15.85, this doesn't change with the number of floors (number of floors is the only variable)
each floor is 3.9 meters, so 3.9 times number of floors
function is f(n)=3.9n+15.85
( just for fun it can be simplified into f(n)=3.9(n+4.0641))

the function is f(n)=39n+15.85

second problem
domain is the set of numbers you can put into the function

range is the set of numbers you get from the numbers in the domain when put into the function (like the solution or result)

so if x=-7 then f(x)=-9
the range is obviously all the numbers on the right
range=-9,-4,-1

answers:
18:  f(n)=3.9n+15.85
19:  range=-9,-4,-1

The mode is the most frequently occurring value.