Ответ:

R=Ro*(1+α*t)

R1=Ro*(1+α*t1)

R1/R=(1+α*t1)/(1+α*t)

t1=(R1*(1+α*t)/R — 1)/α=(18*(1+0.006*10)/15 — 1)/0.006=45.3 °C

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