3*(х+3) =4*(х-3)
3х+9=4х-12
3х-4х=-12-9
х=21=собственная скорость
s=3*(21+3)=72 км
y = 3^x, x + y = 4, x = 0, y = 0. S = ? x + y = 4 => y = 4 - x.