Answer:
Cost of one book = $61
and cost of another book =$17
Step-by-step explanation:
Let the cost of one book be x and cost of another book be y.
According to given problem,
x = 3y+4 {one book cost four dollars more than three times the other}
And x + y =72 {two books cost $72}
So we got two equations:
x = 3y+4 -------------(1)
x + y = 72 ---------------(2)
Subtract equation (1) from (2)
i.e x + y - x = 72 - 3y -4
or y = 68 - 3y
or y +3y =68
or y =
or y = 17
Then x = 3y + 4 = 3×19 + 4 =61
Hence we got, cost of one book = x =$61
Cost of another book = y = $17