In this Linear function given by the law d(t) = 12t +20 and the graph below. To find the d(4), means to find out how many miles she cycled in the instant 4 hours.
By this function, after a break , the instant t=0, she had already cycled 20 miles.
If we assume the number of polo shirts have been sold is x, the number of casual shirts have been sold will be 4x. x*18+4x*9=$1080 (18+36)x=$1080 54x=$1080 x=20
The number of casual shirts have been sold is 4*20=80
