Test if W = {(X, Y, Z) / Z = XY; X, Y, Z belongs to R} is a subspace of R ^ 3

Two corresponding sides of two similar triangles are 3cm and 5cm. the area of the first triangle is 12cm2. what is the area of the second triangle?

On ryan's last social studies test there were two types of questions true/false worth 3 points each and multiple choice questions worth 4 points each

What is the slope of any line parallel to the line 8x+9y=3 in the standard (x, y) coordinate plane?