This may be a bit awkward to explain in writing, so please bear with me:)
You are given the equations. Begin by focusing on ad = 11.6. Treating variables normally, this reads as a times d = 11.6.
From that, d = 11.6/a by dividing both sides by a.
With d expressed, substitute (11.6/a) into cd = 6.7. Then isolate c by multiplying both sides by a/11.6, yielding c = (6.7a)/11.6.
Now that c is known, insert (6.7a)/11.6 for c in bc = 8.3. The algebra becomes a bit messy, but solving for b gives approximately 14.3705 / a. Since you need ab, multiply both sides by a, and rounding to one decimal place produces ab = 14.4