a)
a_1 : a = 1 : 2
\frac{a_1}{6}=\frac{1}{2}
2a_1=6
a_1=3[cm]
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\frac{b_1}{4}=\frac{1}{2}
b_1=\frac{4}{2}
b=2[cm]
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\frac{c_1}{8}=\frac{1}{2}
c-1=\frac{8}{2}
c_1=4[cm]
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b)
a_1 : a = 3 : 1
\frac{a_1}{6}=\frac{3}{1}
a_1=6*3=18[cm]
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\frac{b_1}{4}=3
b_1=3*4=12[cm]
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\frac{c_1}{8}=3
c_1=3*8=24[cm]