Step-by-step explanation:
let no. of hours be x.
45x - 12 ≥ 117
45x ≥ 129
x ≥ 2.8667 (5sf)
therefore, 3 hours (round up to next whole number).
Topic: inequalities
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Make them both improper fractions.
77/10 - 19/5
Give them common denominators (multiply the second fraction by 2)
77/10 - 38/10
Subtract
39/10 = 3 9/10
Step-by-step explanation:

I hope it makes sense
:)
Answer:
B. 200 doses
Step-by-step explanation:
Given,
1 dose is required for 100 mg,
Since, 1 mg = 0.001 g,
⇒ 100 mg = 0.1 g
⇒ 1 dost is required for 0.1 g,
Thus, the ratio of doses and quantity ( in gram ) is 
Let x be the doses required for 20 grams,
So, the ratio of doses and quantity is 


Hence, 200 doses can be obtained from 20 grams of the drug.
Option 'B' is correct.