Two boys, Unopa and Kagiso, ran a 100 m race. Unopa took r seconds to complete the race.

(a) Write down an expression for his average speed in terms of t.

(b) Kagiso arrived I second later. Write down an expression for his average speed in terms of 1.

(c) If their average speeds differ by 0.12 m/s, form an equation in rand show that it reduces to 3r²+3r-2500=0.​