Pretty much trade. You give vendor money or currency in return they give you the thing you paid for.
D. (7,0)
The original coordinates were (0,7)y and (1,5)x then I rotated it 90 degrees and the coordinates were (7,0)y and (5,1)x
Negative 1 because 3 x 3 is 9 and -2 x 5 is -10. Therefore 9-10= negative 1
Maybe try using a converter
It will need 1.8 kilograms to have 25.0 g of nickel