4. Two music teachers own a studio where they give lessons. The following expressions give the cost, C, for each music teacher after h, the number of hours
Piano:
Drums:
C = 20h + 40
C = 15h + 100
a) Write a simplified combined (HINT: addition) expression representing the cost for having two
music teachers at once. (T 4)
b) If Naomi hires both music teachers for 5 hours, how much will she pay? [T 3]

i believe the correct answer is b.

answer: c, the green line

step-by-step explanation:

there is no black line, eliminate b.

simple interest implies periodic payments, but the red line shows no payments, eliminate d.

simple interest has equal payments. if paid say every day, the graph is about a straight line (actually a stairstep).

the yellow line is not straight, eliminate a.

check: the green line is straight, answer is c.

simple interest with positive interest rate gives a straight line sloping up to the right. green line:

g(t) = $100 + ($200-$100) ÷ (20 years) × (t years)

= $100 + (4%/year) × ($100)(t years)

incidentally, the yellow line curving upward represents continuously compounded interest

y = $100 × 2^(t years / (14 assuming the yellow line hits $200 at 14 years. 2^0 is 1, so y(0) = $100; 2^(14/14) is 2, so y(14) = $200.