Given the system of equations:
-10x-15y=25...................................equation 1
x - 5y = -9.....................................equation 2
Let's solve using substitution method.
From equation 2, make x the subject:
x = -9 + 5y
Substitute (-9 + 5y) for x in equation 1:
-10(-9 + 5y) - 15y = 25
-10(-9) - 10(5y) - 15y = 25
90 - 50y - 15y = 25
90 - 65y = 25
Subtract 90 from both sides:
90 - 90 - 65y = 25 - 90
-65y = -65
Divide both sides by -66