Ответ: c = c1(1 + αt)Q=(c(t1)+c(t2))/2*m*(t2-t1)=M*c_v*(t1-t0)M=(c(t1)+c(t2))/2*m*(t2-t1)/(c_v*(t1-t0)) = c((t1+t2)/2)*m*(t2-t1)/(c_v*(t1-t0)) = = c(80)*m*(100-60)/(c_v*(60-20)) = c1*(1 + α*80)*m*(100-60)/(c_v*(60-20)) = = 1,4*10^3*(1 + 0,014*80)*1*(100-60)/(4200*(60-20)) кг  =
0,706667
кг ~
0,71
кг