Therefore, the figures given by Fischer as to what defendant expected to make during the three months involved' were not based on proof of actual facts which present data for a rational estimate of such profits. No facts nor data were presented but only a speculative expectation or hope with no figures from which any computation could be made. See Kopff v. Deves, Mo.App., 324 S.W.2d 768. Without figures showing what the break-even point' was for this period, there is nothing from which even to start a computation. Fischer said the break-even point was not even figured on a monthly basis, but on a quarterly basis, yet he stated definite amounts of expected profits for each month. There is nothing in the record to support any of these estimates. In Hargis v. Sample, Mo.Sup., 306 S.W.2d 564, relied on by defendant (loss of profits from untenantable hotel rooms) there was evidence of an estimated number of rooms not rentable, ■showing stated prices, the number of people turned away and the cost of supplying the rooms. We held the amount of damages could be estimated from such facts but said they should be more accurately established on retrial. Defendant also cites Giudicy v. Giudicy Marble, Terrazzo & Tile Co., Mo.Sup., 329 S.W.2d 664, an action for royalties, in which we held testimony as to method used to determine quantity of rock removed was sufficient to sustain the finding as to the quantity actually removed. In that case also facts were shown which presented data for a. rational estimate, so these cases do not help defendant. The question of whether an opinion of an expert is based on and supported by sufficient facts to sustain it, is a question of law for the court. Hall v. Mercantile Trust Co., 332 Mo. 802, 59 S.W.2d 664; for other cases see West’s Missouri Digest, Evidence, t®==’555. We hold it was error to allow Fischer to state his conclusion as to expected monthly profits, without any facts being shown upon which to base it, and that such conclusion was not substantial evidence to show lost profits.