急!數學問题,幫下我啦,答小小都好 20點

1. The result of subtracting the triple of a number from 51 is 30.find the number.
Solution:
Let n be the number.
51-3n=30
-3n=-21
n=7
∴The number is 7.
2.the result of subtracting 18 from the perimeter of a square is 26.find the lenght of each side of the square.
Solution:
Let l be the lenght of each side of the square.
4l-18=26
4l=44
l=11
∴The length of each side of the square is 11.
3.if the sum of two consecutive even number is 86,find the smaller number.
Solution:
Let x be the smaller number.
x+(x+2)=86
2x=84
x=42
∴The smaller number is 42.

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