數學問題!!!!唔識做!!!!急急急急!!!!

Q1)Stephanie and Dennis go hiking together. They go uphill at a speed of 3 km/h and downhill at a speed of 4 km/h. If the lengths of the downhill paths are the same, and Stephanie and Dennis speed a total of 4.2 hrs in completing their journey, find the total length of the journey.
Let length of uphill path = length of downhill path = d (in hour)
Time going uphill = d/(3 km/h)
Time going downhill = d/(4 km/h)

Time going uphill + time going downhill = 4.2 h
d/3 + d/4 = 4.2
Multiplied by 12
12(d/3) + 12(d/4) = 12(4.2)
4d + 3d = 50.4
7d = 50.4
d = 50.4/7 = 7.2 km
Total length of the journey = 7.2 km x 2 = 14.4 km

Q2)In a two-digit no.,the units digit is greater than the tens digit by 3.If the tens digit and the units digit of the no. are interchanged,the sum of the no. obtained and the original no. is 121.find the two no.s.(hints:14=1x10+4,41=4x10+1)
x – y = 3, x = y + 3 ----------- (1)
(10x +y) + (10y +x) = 121 -------- (2)
substitute (1) into (2)
10(y+3) +y + 10y +y+3) = 121
10y+30 +y + 10y +y +3) = 121
22y + 33 = 121
22y = 121 -33 =88
y =88/22 = 4
x = y + 3 = 4+3 = 7
The two numbers are 74 and 47

Q3)Daniel sells some jackets with a marked price of $200each.

A)Without any discount,it is known that each jacket is sold at a profit of 60%.Find the cost of each jacket.
Mark price of jacket = cost of jacket x 160%
$200 = cost of jacket x 1.60
Cost of jacket = $200/1.6 = $125

B)If Daniel sells the jackets at 40% off,find the %profit/loss of selling each jacket.
Selling price = Mark price (100% – 40%)
Selling price = $200 x (60%) = $200 x 0.6 = $120
Profit/Loss = selling price – cost = $120 - $125 = -$5 (Negative value indicates it is a loss.
% loss = loss/cost x 100% = $5/%125 x 100% = 4%
% loss = 4%

C)After offering a discount, the jackets are still sold at a profit of 28%.Find the%discount offered.
Profit/cost x 100% = 28%
Profit/$125 = 0.28
Profit = $35
Selling price = cost + profit = $125 + $35 = $160
Discount % = [($200 - $160)/$200] x 100% =($40$/200) x 100% = 20%
The % discount = 20%