This is not a word problem and is ambiguous.  'sqt' can either be interpreted as 'the square root of' or the intention is to solve for 'sqt'. 

One could take rqt=9x+54, solve for 'r' and then substitute 'r' from 'rqs=7x+7' in order to obtain 's', 'q' and 't'. 

rqt=5x+54

click here to solve for r

r=((9(x+6))/(qt)

The substitution of 'r' would obtain:

(((9(x+6))/(qt))qs=7x+7

....but solving for 'sqt' would not be feasible