Can someone please help me I dont understand how to do these!!!???

Question 1:

20% of what number is 90.

Number: 450

Work:

20% × x = 90

multiply both sides by 100 and divide by 20

90 x 100/20

9000/20 = 450

x = 450

Question 2:

60% of what number is 150

Number: 250

Work:

60% × x = 150

multiply both sides by 100 and divide by 60

150 x 100/60

15000/60 = 250

x = 250

Question 3:

Pages: 144

Work:

.8 x 180 = 144

Question 4:

Full dose: 800 mg

75% = 3/4  

Work:

600 = 3/4  

600 (4/3) = 3/4(4/3)  

2400/3 = 1  

800 = 1  

600 is 75% of 800.

Question 5:

18

Work:

(20 x 90)/100 = 1800

1800/100 = 18

step-by-step explanation:

what grade level is this? need to know so i can look in my old textbooks!