Need with both question. grateful for any .

18) 
It says the scale factor is 1:25000, so for every one part there is actually 25000. So for every centimeter, there is actually 25000 cm. See that we multiplied by 25000. 
So for 6.8cm, multiply by 25000 to get 170000cm. 
The real distance represented is 170000cm.

19) Just work out one step at a time using order of operations. 
Do parentheses first. 7^2 = 49, and 3^3 is 3*3*3 which is 27. 
Now you have [8(49 - 27) ]/ sqrt121. 

Finish simplifying the parentheses. 49 - 27 is 22.
[8(22)] / sqrt121.

Now multiply 8 times 22, which is 176.
176 / sqrt 121 

The square root of 121 is 11.

176/11.
= 16

#18).

-- The map has a scale factor of 1:25,000.

-- Any distance on the paper map represents
25,000 times that distance in the real world.

-- If you measure 6.8 cm on the paper map,
that represents a real distance of    (25,000 times 6.8 cm).

#19).  Relax, breathe, and take it one step at a time:

=>  7² = 49
=>  3³ = 27
=> (7² - 3³) = (49 - 27) = 22
=>  8 times that is  176 .

√121  =  11 .

Can you handle it from there ?