(0.4x -2y)/(0.3x²-7.5y²),
1) 0.4x -2y =0.4(x -5y)
2) 0.3x² -7.5y² =0.3(x² -25y²) =0.3(x -5y)(x +5y)
3) 0.4(x-5y) /0.3(x-5y)(x+5y) =0.4 /0.3(x +5y)
4) x +5y =4
0.4 /(0.3*4) =0.4 /1.2 =4/10 :12/10 =4/10 *10/12 =(4*10) /(10*12) =4/12 =1/3
ответ: номер 1) 1/3