The correct option is C 81p+49q+64r
In option (a.), we have 3×(a+b)+6ab+8a. on opening the bracket we get 3a+3b+6ab+8a. Now, we clearly see that 3a and 8a are like terms and hence, given expression can be simplified to 11a+3b+6ab.
In option (b.), we have 5x+4y+7×(x+y).
on opening the bracket we get 5x+4y+7x+7y. Now, we clearly see that 5x and 7x; 4y and 7y are like terms and hence, given expression can be simplified to 12x+11y.
In option (c.), we have 81p+49q+64r. As all of the terms in this algebraic expression are unlike terms, it cannot be simplified any further.
In option (d.), we have −1+3+5+6m. This algebraic expression can be further simplified by adding the constant terms together. i.e. −1+3+5+6m=6m+7
Therefore, only the expression given in option(c.) cannot be further simplified.