Answer:
C
Step-by-step explanation:
The multiples of 3 are
3, 6, 9, 12, 15, ...........
The terms form an arithmetic sequence with common difference of 3.
The sum to n terms is
= 
[2a₁ + (n - 1)d ]
where a₁ is the first term and d the common difference
Here a₁ = 3 and d = 3, thus
= 
[ (2 × 3) + (139 × 3) ]
= 70(6 + 417) ] = 70 × 423 = 29610 → C
STEP 1:
convert meters to centimeters
100 cm= 1 meter
= 100 cm/m * 2.5 m
= 250 cm
STEP 2:
x= length of first shelf
2x+18= length of second shelf
x-12= length of third shelf
x+4= length of fourth shelf
since the whole board has to be used, add lengths of all shelves and set it equal to the whole length of the board (250 cm).
x + (2x+18) + (x-12) + (x+4)= 250 cm
combine like terms
5x + 10= 250
subtract both sides by 10
5x= 240
divide both sides by 5
x= 48
STEP 3:
find length of second shelf
= 2x + 18
= 2(48) + 18
= 114 cm
CHECK:
x + (2x+18) + (x-12) + (x+4)= 250
48 + (2(48)+18) + (48-12) + (48+4)= 250
48 + (96+18) + 36 + 52= 250
48 + 114 + 36 + 52= 250
250= 250
ANSWER: Shelf two is 114 cm.
Hope this helps! :)
4.3x+5x=16+7-(7)
9.3x=16
x= 1.72
give me a brainliest if possible. please.. tnx
4 is correct. Set up a ratio relationship between similar triangles. 
