You can use gauss's method
n(first number + last number)/2 where n is the number of integers in this case 21 ()
21(0.30 + 0.50)/2
21*0.8/2
21*0.4
8.4
<span><span><span>(x−a)</span>2</span>+<span><span>(y−b)</span>2</span>=<span>r2 I think.
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Solve for positive 72 and separate the negative part as
The rest of calculation is same..
1a, 64/4=16 x=16cm
1b, 2(5x+2x)=98
2(7x) =98
14x=98
x=7
1c, 5(x+4)=45
5x+20=45
5x=25
x=5