B and T are the numbers of bushes and trees.
15B+18T=975; 5B+6T=325; 7B+5T=470. T=(470-7B)/5. Substitute in the other equation:
15B+18(470-7B)/5=975; 75B+8460-126B=4875; 51B=8460-4875=3585; B=3585/51=1195/17=70.29.
T=(470-7*1195/17)/5<0, so there is an error.
Please check the facts and figures in the question.