the gradient of a line is another word for the slope, namely the change in y coords over the change in x. it can be derived from the standarrd equation of a line, namely y = mx +b, where b is the gradient.

For the last one, think of the defnition of being pependicilar (they intersect at a right angle, the slope of one line = the negative inverse of the other)

good work on the other problems btw