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75% x X + 3/4 x X + X = 30
75/100 x X + 3/4 x X + X x 1 = 30
0,75 x X + 0,75 x X + X x 1 = 30
X x ( 0,75 + 0,75 + 1 ) = 30
X x 2,5 = 30
X = 30 : 2,5
X = 12
\(75\%.x+\frac{3}{4}.x+x=30\)
\(\frac{3}{4}.x+\frac{3}{4}.x+x=30\)
\(x.\left(\frac{3}{4}+\frac{3}{4}+1\right)=30\)
\(x.\frac{5}{2}=30\)
\(x=30:\frac{5}{2}\)
\(x=12\)