The temperature, θ∘C\theta^\circ\text{C}θ∘C, of a cup of tea t t\,t minutes after measurements began, is modelled using the formula θ=68e−0.15t+21,t≥0\theta = 68e^{-0.15t} + 21, t \geq 0θ=68e−0.15t+21,t≥0
Sketch the graph of θ \theta\,θ against ttt.
Find according to the model the initial temperature of the tea.
Find the value of t t\,t when the cup of tea reaches 40∘C40^\circ\text{C}40∘C.
