Isolate the x. Do the opposite of PEMDAS. Note the equal sign, what you do to one side, you do to the other.
First, subtract 8 from both sides
8 (-8) + 7x = -61 (-8)
7x = -69
Next, isolate the x. Divide 7 from both sides
7x/7 = (-69)/7
x = -69/7
x = ~-9.86 (rounded)
hope this helps