Respuesta :

dH/dt=-4/5
dH=-4/5dt
H= ∫-4/5dt
H= -4/5t+c
c= 4/5×3= 12/5
so
H=-4/5t+12/5
at first minute i.e T= 1
H= 12/5-4/5
H= 8/5 = 1.6mile
Q&A Education