You need to know these two formulas:

For example,

I think it is the 3rd one but I might be wrong...
Answer:
8
Step-by-step explanation:
8y-3y=40
5y. = 40
y. =8
the value of y is 8.
...
Answer:
90
Step-by-step explanation:
Step-by-step explanation:
The hands of a clock point in opposite directions ( in the same straight line) 11 times in every 12 hours.