Question 135235
Use FOIL -- First, Outside, Inside, Last


{{{(x - 4y)( 5x - 9y)}}}


First: {{{x * 5x = 5x^2}}}
Outside: {{{x * -9y= -9xy}}}
Inside: {{{-4y * 5x = -20xy}}}
Last: {{{-4y * -9y = 36y^2}}}


Add 'em up:
{{{5x^2-9xy-20xy+36y^2}}}


Collect like terms:
{{{5x^2-29xy+36y^2}}}

Done.