find the gradient first using

m= y-y1 / x-x1 (minus y values from each other the minus x values )

-1+19 / 2+4 therefore m= 18/6 so m = 3 which is your gradient

then choose one of your 2 points so for eg (2,-1)

then use y= mx+c

-1= 3 (2) + c

-1 = 6+c

c = -7

the equation is y= 3x-7

you can solve the part 2 the same way. to find where the lines intersect, make them equal to each other then find x and y.