#(1) " "#Change the sum to a multiplication by inverting the second fraction .
#(2x-3)/(x^2-16)-:(8x-12)/((4-x)#
#=(2x-3)/(x^2-16)xx(4-x)/(8x-12)#
#(2)" "#Now factorise where possible
#=(2x-3)/((x-4)(x+4))xx(-(x-4))/(4(2x-3))#
#(3)" "#Cancel where possible
#=cancel(color(red)((2x-3)))/(cancel(color(blue)((x-4)))(x+4))xx(-cancel(color(blue)((x-4))))/(4cancel(color(red)((2x-3))))#
#=-1/(4(x+4)#