If you represent the problem in a diagram, you will form a triangle with 3 known length of the sides. When you are given all sides, and you are asked to find an angle, you can use the cosine law.
b^2 = a^2 + c^2 - 2ac*cosB
1.4^2 = 1.9^2 + 1^2 - 2(1.9*1)(cosB)
B = 45.78°
23.4375 or 24.0 is the bacteria count after 6 hours.
Y=2x+6
gradient is found from the formula,

y intercept is found by subbing the values of (-1,4) into the equation y=2x+c
Step 1: Find X
3x + 7 + 9x + 17
Add the alike terms: 12x + 24
Linear is 180 degree, 12x + 24 = 180; now find x
X = 13
Now find the degree for both.
RST: 3 (13) + 7 = 46
VST: 9 (13) + 17 = 134
You're answer is A