Question

x-3 supra 15=6 supra 5
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Answer 1

faci egalitatea dintre produsul mezilor si extremilor, adica 5(x-3)=15x6, deci 5x-15=90, sau 5x=105, rezulta x=105:5=21

Answer 2

$\displaystyle \frac{x-3}{15} = \frac{6}{5} \\ \\ \\ x-3 = \frac{\not15\cdot6}{\not5} = \\ \\ \\ x-3= 3 \cdot 6 \\ \\ \\ x-3=18 \\ \\ \\ x=18+3 \\ \\ \\ x=21$