A young sumo wrestler decided to go on a special high-protein diet to gain weight rapidly. He gained weight at a rate of $5.5$ kilograms per month. After $11$ months, he weighed $140$ kilograms. Let $W(t)$ denote the sumo wrestler's weight $W$ (measured in kilograms) as a function of time $t$ (measured in months). **Write the function's formula.** $W(t)=$ [[☃ expression 1]]