Answer:
The different variable in C is 21213316700.
Explanation:
Given value:
Total value = letters + underscore value
Total value = 52 + 1
Total value =53
choice for first character = 53 letters +10 digits
first character = 63
choice for remaining characters
So,
Variable number With one 1 character = 53
Variable number With 2 character = 53 × 63
Variable number With 3 character = 53 × 63²
Variable number With 4 character = 53 × 63³
.
.
.
Variable number With 7 character = 
Total difference variable = 53 + 53 × 63+ 53 × 63²+ 53 × 63³+....+ 
Total difference variable = 53(1 + 63 + 63²+ 63³+ .... +
)
Formula:

Total difference variable

Answer:
A. set_union
Explanation:
The algorithm set_union is used to find the elements in one range of elements that do not appear in another range of elements.
Length of the boat is the factor that determines a boat's
required equipment.
<span>Safety required equipment are the most important on the
boat or vessel, and an operator of the boat must make sure that a boat has
safety equipment. According to the length of the boat equipment are required, if
the boat is large in length, it contains more equipment than the boat which is
small in length.</span>
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