Let's solve the equation step by step:

Distribute the 5 on the left side:
55x - 155 - 9x = 121(8x + 91) / 7 = 21

Combine like terms on the left side:
46x - 155 = 968x + 1091 / 7 = 21

Multiply both sides by 7 to get rid of the denominator:
7(46x - 155) = 968x + 1091

Distribute the 7 on the left side:
322x - 1085 = 968x + 1091

Rearrange the equation by moving variables to one side:
322x - 1085 - 968x = 1091

Combine like terms:
-646x - 1085 = 1091

Add 1085 to both sides:
-646x = 2176

Divide by -646 to solve for x:
x = -2176 / 646

Therefore, x = -3.37.