A) To solve the equation X - 6/4 = (7/2)^8 × (7/2)^7, we can simplify the right side first.

(7/2)^8 × (7/2)^7 = (7/2)^(8+7) = (7/2)^15

Now, we can rewrite the equation as:

X - 6/4 = (7/2)^15

To simplify the left side, we need to convert 6/4 to a fraction with the same denominator as 2:

6/4 = 3/2

Now, the equation becomes:

X - 3/2 = (7/2)^15

To isolate X, we can add 3/2 to both sides:

X - 3/2 + 3/2 = (7/2)^15 + 3/2

X = (7/2)^15 + 3/2

B) To solve the equation (156 + X) - 48 = 615, we can simplify the left side first.

(156 + X) - 48 = 615

156 + X - 48 = 615

To isolate X, we can subtract 156 from both sides:

156 + X - 48 - 156 = 615 - 156

X - 48 = 459

To isolate X, we can add 48 to both sides:

X - 48 + 48 = 459 + 48

X = 507

C) To solve the equation 86 : X + 15 = 678, we can simplify the left side first.

86 : X + 15 = 678

To isolate X, we can subtract 15 from both sides:

86 : X + 15 - 15 = 678 - 15

86 : X = 663

To isolate X, we can multiply both sides by X:

(X)(86 : X) = (663)(X)

86 = 663X

To isolate X, we can divide both sides by 663:

86/663 = 663X/663

X = 86/663