Could you help me answer this question? And what does the sign of the slope estimated for an interaction term (e.g., the positive value of 1.7 in the question) tell us?

Imagine again you own that antique shop and you have a new idea that, actually, condition might moderate the effect of age on price. You fit a regression model predicting the price (Y measured in dollars) a piece will sell at from its age (X , measured in years), its weight (X2 in pounds), its condition (X3 on an interval-level 1-10 scale where 10 is perfect and 1 is terrible condition), and the interaction between age & condition. Your estimate the best fitting multiple regression equation to be: y = 2.53x1 + 0.5x2 + 25x3 + 1.7x1x3+ 20 On your next trip to antique country you spot a 125-year-old vase that weighs 5 pounds and you rate at a 3 for condition. According to your model, what is the predicted price you could sell this for