6th-Grade Math Word Problems - ThoughtCo To solve the first equation on the worksheet, use the basic formula: rate times the time = distance, or r * t = d. In this case, r = the unknown variable, t = 2.25 hours, and d = 117 miles. Isolate the variable by dividing "r" from each side of the equation to yield the revised formula, r = t ÷ d.