Find p in this equation with (0, 50)

2x–(3p+4)y+5p+9 = 0    simplify

2x - 3py - 4y + 5p + 9  = 0  ....  and we want x =0  and y  = 50...so we have

2(0)  - 3p(50)  - 4(50)  + 5p   + 9   = 0 

0 - 150p - 200 +  5p  + 9  = 0

-145p - 191  = 0    add 191 to both sides

-145p   = 191     divide both sides by -145

p =   -191/ 145

Proof :

2x - (3 (-191/145) + 4)y  + 5(-191/145) + 9   = 0

2x - [7/145 ] y  - 955/145  + 9  = 0

2x - [7/145]y  - 955/145 + 9  = 0          and when x = 0 and y = 50, we have

2(0) - [7/145] (50)  - 955/145  + 9  = 0

-[7 /145] (50)  +  70/29  =0

-7(50) /145 + 70/29  =0

-7 (10)/29 + 70/29

-70/29 + 70/29  = 0