Answer:
a ) 400 percent
b ) n = 25
c) n= 36
Step-by-step explanation:
Is means equals, of means multiply and percents need to be changed to decimals.
a) 120 is what percentage of 30
120 = P * 30
Divide each side by 30
120/30 =P* 30/30
4 = P
Multiply by 100 to give the percentage
4 * 100
400 percent
b) 30 is 120% of what number
30 = 1.2 * n
Divide each side by 1.2
30/1.2 = 1.2n/1.2
25 = n
c) what number is 30%of 120
n = .3 * 120
n =36
A unit rate simply means how many of one type of units you get per 1 other type of unit.
Examples of that:

This is rate of fluid flow of some pump for example. It pumps 300 liters every second.
Other example:

This is example for speed. Somebody is moving at 50 kilometers per hour (every hour he travels 50 kilometers)
For the first blank, the answer should be the total weight of the solution which is derived from adding 5 grams and 20 grams. The answer would be,
T = 5 + 20 = 25 grams
For the second blank, the % solution is derived by dividing the amount of salt initially by the total amount of the resulting solution. This is as shown below.
C = ((20 x 0.5) / 25) x (100%)
Simplifying,
C = 40%
Answers:
a. 25 grams
b. 40%