Step 1) Because the first equation is already solved for #y# we can substitute #(7x - 51)# for #y# in the second equation and solve for #x#:
#y = -3x + 29# becomes:
#7x - 51 = -3x + 29#
#color(blue)(3x) + 7x - 51 + color(red)(51) = color(blue)(3x) - 3x + 29 + color(red)(51)#
#(color(blue)(3) + 7)x - 0 = 0 + 80#
#10x = 80#
#(10x)/color(red)(10) = 80/color(red)(10)#
#(color(red)(cancel(color(black)(10)))x)/cancel(color(red)(10)) = 8#
#x = 8#
Step 2) Substitute #8# for #x# in the first equation and calculate #y#:
#y = 7x - 51# becomes:
#y = (7 xx 8) - 51#
#y = 56 - 51#
#y = 5#
The solution is: #x = 8# and #y = 5# or #(8, 5)#
